Rollup merge of #124169 - compiler-errors:parser-fatal, r=oli-obk

Don't fatal when calling `expect_one_of` when recovering arg in `parse_seq`

In `parse_seq`, when parsing a sequence of token-separated items, if we don't see a separator, we try to parse another item eagerly in order to give a good diagnostic and recover from a missing separator:
https://github.com/rust-lang/rust/blob/d1a0fa5ed3ffe52d72f761d3c95cbeb0a9cdfe66/compiler/rustc_parse/src/parser/mod.rs#L900-L901

If parsing the item itself calls `expect_one_of`, then we will fatal because of #58903:
https://github.com/rust-lang/rust/blob/d1a0fa5ed3ffe52d72f761d3c95cbeb0a9cdfe66/compiler/rustc_parse/src/parser/mod.rs#L513-L516

For `precise_capturing` feature I implemented, we do end up calling `expected_one_of`:
https://github.com/rust-lang/rust/blob/d1a0fa5ed3ffe52d72f761d3c95cbeb0a9cdfe66/compiler/rustc_parse/src/parser/ty.rs#L712-L714

This leads the compiler to fatal *before* having emitted the first error, leading to absolutely no useful information for the user about what happened in the parser.

This PR makes it so that we stop doing that.

Fixes #124195

Author: matthiaskrgr