doc/next: organize 9-todo.md items by category

Most items that need to be done are tracked in release-blocking issues,
but a few are not. Make it easier to understand and track their status.

For #68545.

Change-Id: I1cb31e67d2d868a82ee592c9adb31bc5dd558d67
Reviewed-on: https://go-review.googlesource.com/c/go/+/632195
Reviewed-by: Dmitri Shuralyov <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: dmitshur

doc/next/2-language.md

@@ -1,5 +1,6 @@
 ## Changes to the language {#language}
 
+<!-- go.dev/issue/46477 -->
 Go 1.24 now fully supports [generic type aliases](/issue/46477): a type alias
 may be parameterized like a defined type.
 See the [language spec](/ref/spec#Alias_declarations) for details.

doc/next/3-tools.md

@@ -15,7 +15,7 @@ a test integration system, you can revert to the text build output by setting
 
 ### Cgo {#cgo}
 
-<!-- go.dev/issue/56378 -->
+<!-- go.dev/issue/56378, CL 579955 -->
 Cgo supports new annotations for C functions to improve run time
 performance.
 `#cgo noescape cFunctionName` tells the compiler that memory passed to

doc/next/6-stdlib/5-sha3.md

@@ -1,5 +1,6 @@
 ### New sha3 package
 
+<!-- go.dev/issue/69982, go.dev/issue/65269, CL 629176 -->
 The new [crypto/sha3] package implements the SHA-3 hash function, and SHAKE and
 cSHAKE extendable-output functions.