Replace - with _ in ftl slugs for better grepability

Having to replace - with _ (and vice versa) makes the slugs less greppable
and thus constitutes a contributor roadblock.

Result of running this repeatedly up until reaching a fixpoint:

find compiler/rustc_error_messages/locales/en-US/ -type f -exec sed -i 's/\(.+\)-\(.*\)=/\1_\2=/' {} \;

Plus some fixes to update usages of slugs leading with -.

Author: est31

compiler/rustc_error_messages/locales/en-US/borrowck.ftl

@@ -1,18 +1,18 @@
-borrowck-move-unsized =
+borrowck_move_unsized =
     cannot move a value of type `{$ty}`
     .label = the size of `{$ty}` cannot be statically determined
 
-borrowck-higher-ranked-lifetime-error =
+borrowck_higher_ranked_lifetime_error =
     higher-ranked lifetime error
 
-borrowck-could-not-prove =
+borrowck_could_not_prove =
     could not prove `{$predicate}`
 
-borrowck-could-not-normalize =
+borrowck_could_not_normalize =
     could not normalize `{$value}`
 
-borrowck-higher-ranked-subtype-error =
+borrowck_higher_ranked_subtype_error =
     higher-ranked subtype error
   
-generic-does-not-live-long-enough =
+generic_does_not_live_long_enough =
     `{$kind}` does not live long enough

compiler/rustc_error_messages/locales/en-US/builtin_macros.ftl

@@ -1,5 +1,5 @@
-builtin-macros-requires-cfg-pattern =
+builtin_macros_requires_cfg_pattern =
     macro requires a cfg-pattern as an argument
     .label = cfg-pattern required
 
-builtin-macros-expected-one-cfg-pattern = expected 1 cfg-pattern
+builtin_macros_expected_one_cfg_pattern = expected 1 cfg-pattern

compiler/rustc_error_messages/locales/en-US/const_eval.ftl

@@ -1,31 +1,31 @@
-const-eval-unstable-in-stable =
+const_eval_unstable_in_stable =
     const-stable function cannot use `#[feature({$gate})]`
-    .unstable-sugg = if it is not part of the public API, make this function unstably const
-    .bypass-sugg = otherwise `#[rustc_allow_const_fn_unstable]` can be used to bypass stability checks
+    .unstable_sugg = if it is not part of the public API, make this function unstably const
+    .bypass_sugg = otherwise `#[rustc_allow_const_fn_unstable]` can be used to bypass stability checks
 
-const-eval-thread-local-access =
+const_eval_thread_local_access =
     thread-local statics cannot be accessed at compile-time
 
-const-eval-static-access =
+const_eval_static_access =
     {$kind}s cannot refer to statics
     .help = consider extracting the value of the `static` to a `const`, and referring to that
-    .teach-note = `static` and `const` variables can refer to other `const` variables. A `const` variable, however, cannot refer to a `static` variable.
-    .teach-help = To fix this, the value can be extracted to a `const` and then used.
+    .teach_note = `static` and `const` variables can refer to other `const` variables. A `const` variable, however, cannot refer to a `static` variable.
+    .teach_help = To fix this, the value can be extracted to a `const` and then used.
 
-const-eval-raw-ptr-to-int =
+const_eval_raw_ptr_to_int =
     pointers cannot be cast to integers during const eval
     .note = at compile-time, pointers do not have an integer value
     .note2 = avoiding this restriction via `transmute`, `union`, or raw pointers leads to compile-time undefined behavior
 
-const-eval-raw-ptr-comparison =
+const_eval_raw_ptr_comparison =
     pointers cannot be reliably compared during const eval
     .note = see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information
 
-const-eval-panic-non-str = argument to `panic!()` in a const context must have type `&str`
+const_eval_panic_non_str = argument to `panic!()` in a const context must have type `&str`
 
-const-eval-mut-deref =
+const_eval_mut_deref =
     mutation through a reference is not allowed in {$kind}s
 
-const-eval-transient-mut-borrow = mutable references are not allowed in {$kind}s
+const_eval_transient_mut_borrow = mutable references are not allowed in {$kind}s
 
-const-eval-transient-mut-borrow-raw = raw mutable references are not allowed in {$kind}s
+const_eval_transient_mut_borrow_raw = raw mutable references are not allowed in {$kind}s

compiler/rustc_error_messages/locales/en-US/expand.ftl

@@ -1,5 +1,5 @@
-expand-explain-doc-comment-outer =
+expand_explain_doc_comment_outer =
     outer doc comments expand to `#[doc = "..."]`, which is what this macro attempted to match
 
-expand-explain-doc-comment-inner =
+expand_explain_doc_comment_inner =
     inner doc comments expand to `#![doc = "..."]`, which is what this macro attempted to match

compiler/rustc_error_messages/locales/en-US/lint.ftl

@@ -1,34 +1,34 @@
-parser-struct-literal-body-without-path =
+parser_struct_literal_body_without_path =
     struct literal body without path
     .suggestion = you might have forgotten to add the struct literal inside the block
 
-parser-maybe-report-ambiguous-plus =
+parser_maybe_report_ambiguous_plus =
     ambiguous `+` in a type
     .suggestion = use parentheses to disambiguate
 
-parser-maybe-recover-from-bad-type-plus =
+parser_maybe_recover_from_bad_type_plus =
     expected a path on the left-hand side of `+`, not `{$ty}`
 
-parser-add-paren = try adding parentheses
+parser_add_paren = try adding parentheses
 
-parser-forgot-paren = perhaps you forgot parentheses?
+parser_forgot_paren = perhaps you forgot parentheses?
 
-parser-expect-path = expected a path
+parser_expect_path = expected a path
 
-parser-maybe-recover-from-bad-qpath-stage-2 =
+parser_maybe_recover_from_bad_qpath_stage_2 =
     missing angle brackets in associated item path
     .suggestion = try: `{$ty}`
 
-parser-incorrect-semicolon =
+parser_incorrect_semicolon =
     expected item, found `;`
     .suggestion = remove this semicolon
     .help = {$name} declarations are not followed by a semicolon
 
-parser-incorrect-use-of-await =
+parser_incorrect_use_of_await =
     incorrect use of `await`
-    .parentheses-suggestion = `await` is not a method call, remove the parentheses
-    .postfix-suggestion = `await` is a postfix operation
+    .parentheses_suggestion = `await` is not a method call, remove the parentheses
+    .postfix_suggestion = `await` is a postfix operation
 
-parser-in-in-typo =
+parser_in_in_typo =
     expected iterable, found keyword `in`
     .suggestion = remove the duplicated `in`