`proc_macro::quote` cannot be made useful for rust-analyzer

Macro in question: https://doc.rust-lang.org/proc_macro/macro.quote.html

What do I mean with this? Basically rust-analyzer cannot make use of the spans the macro generated, as these spans are generated and stored (via save_span) at compilation time of the macro, then loaded (via load_span) by the proc macro server when executed. rust-analyzer is not the tool that compiles the proc-macros though, so we are not the one saving any spans and as such we also can't really load them (even if we go through the artifacts produced, their representation differs from our spans). So for r-a to be able to make use of this feature (should it ever get stabilized), the implementation details would need to change in some way and/or r-a needs to be the one compiling the proc-macros somehow.

Start with the linked proc_macro::quote documentation and trace how save_span and load_span are used by the proc macro server. Compare the compiler-produced span artifacts with rust-analyzer's span representation, then define a viable ownership or interchange design that lets rust-analyzer use generated spans.