Auto merge of #107478 - compiler-errors:anon-enum-tys-are-ambiguous, r=estebank

Revert "Teach parser to understand fake anonymous enum syntax" and related commits

anonymous enum types are currently ambiguous in positions like:

* `|` operator: `a as fn() -> B | C`
* closure args: `|_: as fn() -> A | B`

I first tried to thread around `RecoverAnonEnum` into all these positions, but the resulting complexity in the compiler is IMO not worth it, or at least worth a bit more thinking time. In the mean time, let's revert this syntax for now, so we can go back to the drawing board.

Fixes #107461

cc: `@estebank` `@cjgillot` #106960

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### Squashed revert commits:

Revert "review comment: Remove AST AnonTy"

This reverts commit 020cca8d36cb678e3ddc2ead41364be314d19e93.

Revert "Ensure macros are not affected"

This reverts commit 12d18e403139eeeeb339e8611b2bed4910864edb.

Revert "Emit fewer errors on patterns with possible type ascription"

This reverts commit c847a01a3b1f620c4fdb98c75805033e768975d1.

Revert "Teach parser to understand fake anonymous enum syntax"

This reverts commit 2d824206655bfb26cb5eed43490ee396542b153e.

0 files changed, 0 insertions, 0 deletions