allow filename#L<line_number> syntax to open file at specific line

<!-- ⚠️⚠️ Do Not Delete This! feature_request_template ⚠️⚠️ --> <!-- Please read our Rules of Conduct: https://opensource.microsoft.com/codeofconduct/ --> <!-- Please search existing issues to avoid creating duplicates. --> <!-- Describe the feature you'd like. --> to open a file at specific line, current syntax is: ```sh code -g <filename>:<line_number> ``` please _also_ allow: ```sh code -g '<filename>#L<linue_number>' ``` syntax to make it easier for copy and pasting permalinks from github.com, e.g. `code extensions/git/src/protocolHandler.ts#L64`. #### Breaking Change? no, "also" is an operative word here.