Rollup merge of #126811 - compiler-errors:tidy-ftl, r=estebank

Add a tidy rule to check that fluent messages and attrs don't end in `.`

This adds a new dependency on `fluent-parse` to `tidy` -- we already rely on it in rustc so I feel like it's not that big of a deal.

This PR also adjusts many error messages that currently end in `.`; not all of them since I added an `ALLOWLIST`, excluded `rustc_codegen_*` ftl files, and `.teach_note` attributes.

r? ``@estebank`` ``@oli-obk``

Author: workingjubilee