[Bug][move-compiler] Tiny parser degradation with PR 14792

[brmataptos]

🐛 Bug

PR 14792 changes the way comma lists are parsed slightly, causing test case output third_party/move/move-compiler-2/tests/more-v1/parser/unexpected_token_after_ability_function_constraint.exp to get slightly worse. The diff is here:

   ┌─ tests/more-v1/parser/unexpected_token_after_ability_function_constraint.move:4:21
   │
 4 │     fun foo<T: copy & drop>() {}
-  │                     ^
-  │                     │
-  │                     Unexpected '&'
-  │                     Expected one of: '+', '>', or ','
+  │            -        ^ Expected '>'
+  │            │
+  │            To match this '<'

The problem is that subterm parsing ends and recovery is not attempted until at the list level, where either a comma or a > is expected.

This could be addressed by returning expected tokens along with the returned subterm, so that when we reach an impasse we could add those tokens to the list shown to the user. It might involve a widespread change to the parser (returning expected next tokens along with a successfully parsed item), but probably would greatly improve user experience.