Convert LSP URIs into custom URIs

This introduces a custom URI type in core meant to be extended later
if we want to support other schemes. For now it's just a wrapper over a
PathBuf. We use this new URI type to firewall `lsp::Url`. This was
previously done in 8141a4a but using a custom URI type is more flexible
and will improve the way Pickers handle paths for previews in the child
commit(s).

Co-authored-by: soqb <cb.setho@gmail.com>

Cargo.lock

@@ -1331,6 +1331,7 @@ dependencies = [
  "unicode-general-category",
  "unicode-segmentation",
  "unicode-width",
+ "url",
 ]
 
 [[package]]