Properly account for editions in names

This PR touches a lot of parts. But the main changes are changing
`hir_expand::Name` to be raw edition-dependently and only when necessary
(unrelated to how the user originally wrote the identifier),
and changing `is_keyword()` and `is_raw_identifier()` to be edition-aware
(this was done in #17896, but the FIXMEs were fixed here).

It is possible that I missed some cases, but most IDE parts should properly
escape (or not escape) identifiers now.

The rules of thumb are:

 - If we show the identifier to the user, its rawness should be determined
   by the edition of the edited crate. This is nice for IDE features,
   but really important for changes we insert to the source code.
 - For tests, I chose `Edition::CURRENT` (so we only have to (maybe) update
   tests when an edition becomes stable, to avoid churn).
 - For debugging tools (helper methods and logs), I used `Edition::LATEST`.

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