Add -Zannotate-moves for profiler visibility of move/copy operations

This implements a new unstable compiler flag `-Zannotate-moves` that makes
move and copy operations visible in profilers by creating synthetic debug
information. This is achieved with zero runtime cost by manipulating debug
info scopes to make moves/copies appear as calls to `compiler_move<T, SIZE>`
and `compiler_copy<T, SIZE>` marker functions in profiling tools.

This allows developers to identify expensive move/copy operations in their
code using standard profiling tools, without requiring specialized tooling
or runtime instrumentation.

The implementation works at codegen time. When processing MIR operands
(`Operand::Move` and `Operand::Copy`), the codegen creates an `OperandRef`
with an optional `move_annotation` field containing an `Instance` of the
appropriate profiling marker function. When storing the operand,
`store_with_annotation()` wraps the store operation in a synthetic debug
scope that makes it appear inlined from the marker.

Two marker functions (`compiler_move` and `compiler_copy`) are defined
in `library/core/src/profiling.rs`. These are never actually called -
they exist solely as debug info anchors.

Operations are only annotated if the type:
   - Meets the size threshold (default: 65 bytes, configurable via
     `-Zannotate-moves=SIZE`)
   - Has a non-scalar backend representation (scalars use registers,
     not memcpy)

This has a very small size impact on object file size. With the default
limit it's well under 0.1%, and even with a very small limit of 8 bytes
it's still ~1.5%. This could be enabled by default.

Author: jsgf

src/builder.rs

@@ -1069,7 +1069,7 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
             OperandValue::Ref(place.val)
         };
 
-        OperandRef { val, layout: place.layout }
+        OperandRef { val, layout: place.layout, move_annotation: None }
     }
 
     fn write_operand_repeatedly(

src/debuginfo.rs

@@ -19,7 +19,7 @@ use crate::context::CodegenCx;
 pub(super) const UNKNOWN_LINE_NUMBER: u32 = 0;
 pub(super) const UNKNOWN_COLUMN_NUMBER: u32 = 0;
 
-impl<'a, 'gcc, 'tcx> DebugInfoBuilderMethods for Builder<'a, 'gcc, 'tcx> {
+impl<'a, 'gcc, 'tcx> DebugInfoBuilderMethods<'tcx> for Builder<'a, 'gcc, 'tcx> {
     // FIXME(eddyb) find a common convention for all of the debuginfo-related
     // names (choose between `dbg`, `debug`, `debuginfo`, `debug_info` etc.).
     fn dbg_var_addr(