return line/column numbers relative to the macro call's beginning (instead of the file's beginning) in proc macros

[mr-adult]

I'm opening a separate issue from my original issue for consideration. Providing line and column numbers relative to the proc macro start would help me do what I want in my simpleml_macro crate while maintaining good support in rust-analyzer.

Originally posted by @ChayimFriedman2 in #19032 (comment)