Rename by symbol using F2

[aberba]

Its quite handy to have F2 work for renaming a variable or function across all areas its being used. This usually works when the variable or function is selected.

[jaens]

This worked (somewhat) in https://github.com/d-language-server/dls (which is unmaintained, so I moved over to code-d)

The implementation looks pretty uncomplicated, it just does a "find all references" for the symbol, and then textually replaces all the references with the new symbol.

[WebFreak001]

yes, find all references isn't yet implemented in serve-d yet, so once that's implemented a few related features should be easier to implement