Make Goto Diagnostic overlays consistent

[jwortmann]

At the moment, "Goto Diagnostic..." opens a slightly different overlay compared to invoking "Goto Diagnostic in Project..." and selecting a file. Doing the latter will show the filename in the command palette input and when pressing Backspace it will go back to the list of files, which is not the case for "Goto Diagnostic...".

This PR would make both of the commands to show a consistent overlay by adding the file preselected to the input field for "Goto Diagnostic...".

Feel free to discuss or reject if this implementation feels too dubious/hackish...

[jwortmann]

I think I've addressed all comments.

[jwortmann]

I've noticed that it doesn't look very nice if you open just a single file (without workspace folder): instead of the filename it will show "None" in the command palette input. But this is unrelated to this PR, it also happens on the "main" branch if you run "Goto Diagnostic in Project..." in single file mode. It is just more obvious with this PR.

I think the bug is caused by the following:

This is the function which defines the label:

LSP/plugin/goto_diagnostic.py

Lines 135 to 136 in 0267a1a

	def description(self, value: DocumentUri, text: str) -> str:
	return self._project_path(parse_uri(value))

and it calls _project_path, which returns str(project_path( ... )) or path for file: URIs.

LSP/plugin/goto_diagnostic.py

Lines 159 to 163 in 0267a1a

	def _project_path(self, parsed_uri: ParsedUri) -> str:
	scheme, path = parsed_uri
	if scheme == "file":
	path = str(project_path(map(Path, self.window.folders()), Path(path))) or path
	return path

But the project_path function returns None if there is no window folder:

LSP/plugin/goto_diagnostic.py

Lines 263 to 269 in 0267a1a

	def project_path(project_folders: Iterable[Path], file_path: Path) -> Optional[Path]:
	"""
	The project path of `/path/to/project/file` in the project `/path/to/project` is `file`.
	"""
	folder_path = split_project_path(project_folders, file_path)
	if folder_path is None:
	return None

So we end up with str(None) or path, which will display as literal "None", i.e. the or path which is probably meant as a fallback, doesn't work at all.

I guess I can add a fix to this PR.