Upcoming proc-macro ABI breakage

[mystor]

The changes in rust-lang/rust#98189 were just approved, and are likely to land soon, which will change the unstable proc-macro bridge ABI. I figured I'd file a bug to let you folks know about the changes earlier, in case it could help us reduce how long nightly+rust-analyzer remains broken for.

After these patches land I don't currently have any more patches posted which will break the ABI, though I'm experimenting with some other performance improvements and tweaks locally which will also lead to ABI breakage.

[fasterthanlime]

This can probably be closed as per #12803 (comment)

(It'll be "fixed for good" on monday, but there is a version of proc-macro-srv that supports the latest ABI now).