Adopt rust-analyzer

[est31]

https://github.com/rust-analyzer/rust-analyzer

API docs: https://rust-analyzer.github.io/rust-analyzer/ra_ide_api/index.html

Not sure whether it's up to the task yet.

[cuviper]

FYI, rust-lang/rust#43606 is now talking about removing -Zsave-analysis, and they mentioned the LSIF/SCIP output options from rust-analyzer that may be a sufficient alternative for other tools.

[est31]

@cuviper thanks, that's pretty good. Do you know if they support bulk mode, aka dumping everything, instead of going item per item?

[cuviper]

Sorry, I don't know any of the details about that.