fix(lsp): panic on url_to_uri()

[nayeemrmn]

Fixes panic at:

deno/cli/lsp/urls.rs

Line 155 in 7e68cce

Uri::from_str(url.as_str()).unwrap()

Reported by @marvinhagemeister. We don't know how it's reproduced but there is error handling now.

Also get rid of LspClientUrl, it's been made redundant by lsp_types::Uri. Clean up usage of uri / url / specifier in variable and method names.

[dsherret]

LGTM