Codegen/Rust: allow renaming in QL

[redsun82]

This adds a ql.name codegen pragma to change the name of a property on the QL side. This is useful to give more meaningful names than what we get from the generated rust AST.

This is used as an example for MatchExpr.getExpr, renamed to MatchExpr.getMatchedExpr.

[geoffw0]

SGTM.

[hvitved]

I believe Rust uses the terminology scrutinee, so perhaps getScrutinee instead?

[redsun82]

I believe Rust uses the terminology scrutinee, so perhaps getScrutinee instead?

Ah, that is what @paldepind suggested in his request for this, I didn't know it was an official rust terminology. Matched expression seems more immediate to me, but I won't argue with established terminology! Will do

[paldepind]

Thanks a lot @redsun82. This is great and I think this (and doing the same for other getExpr predicates) can make things quite a bit more readable and solve the problem I mentioned here #17918 (comment) (where the getExpr in the CFG AST layer ends up getting shadowed by other getExpr predicates).