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>