Show currently-computed path on saveinput if valid

[tconbeer]

re-use space used by the validation error label

Show fully-resolved path, but try to show it relative to ~ if that works.

e.g.:

• user types ./foo, show ~/projects/data_project/foo if cwd is ~/projects/data_project
• user types ./foo, show /tmp/abc123/foo if cwd is /tmp/abc123

see tconbeer/harlequin#511

[tconbeer]

see this event handler:

textual-textarea/src/textual_textarea/text_editor.py

Lines 1132 to 1139 in a4c3291

	@on(Input.Changed)
	def update_validation_label(self, message: Input.Changed) -> None:
	if message.input.id in ("textarea__save_input", "textarea__open_input"):
	label = self.footer.query_one(Label)
	if message.validation_result and not message.validation_result.is_valid:
	label.update(";".join(message.validation_result.failure_descriptions))
	else:
	label.update("")