Don't introduce a block around y in parsing x' = y

[mlechu]

Closes #59911. ' is generally treated as its own thing in Expr and flisp, but treated as a special type of call in JuliaSyntax. This change makes x' = y parse to the <=1.11 (= (|'| x) y) instead of wrapping the body in a block like we do when parsing f(x) = y.

The special case is fine to me given that it's a more understandable parse, and we're hoping to move away from LineNumberNodes in the future anyway. (I think this was the original reason for the block-wrap for f(x) = y).

Backporting will be a pain. My plan is to get this reviewed, then make a branch backports-x in the separate JuliaSyntax repository and push this change directly to it, then make a version bump PR to this repository's backports-release-x for x in 1.12, 1.13. Suggestions for how to improve this situation are welcome!

[topolarity]

Backporting will be a pain. My plan is to get this reviewed, then make a branch backports-x in the separate JuliaSyntax repository and push this change directly to it, then make a version bump PR to this repository's backports-release-x for x in 1.12, 1.13. Suggestions for how to improve this situation are welcome!

That is generally how it's done - see https://github.com/JuliaLang/Pkg.jl/tree/release-1.12 + #60158 for example

[DilumAluthge]

@mlechu @topolarity I see the backport 1.12 label on this PR. Are you planning on following the process described in #60246 (comment) (which IIUC looks like the correct process)? If so, we should remove the backport 1.12 label from this PR, so that the Backporter script doesn't try to backport it.

[mlechu]

Thanks for the bump. This is also contained by #60641

[KristofferC]

Needs the same process for 1.13?