This isn't exposed in the GUI, but allows users to
set a specific editor command to use when opening
Python files in the external editor.
Use the token <file> to insert the filename, <line>
to insert line number, and <col> to insert the column number.
Eg:
QgsSettings().setValue(
'gui/code-editor/python/external-editor',
'kate -l <line> -c <col> "<file>"')
This allows the editor to be opened in a proper detached process,
avoiding the editor being closed when QGIS is exited.
Move to a blocklist for terminal text editors instead of the fragile
polling approach (which eg doesn't work if the editor is set to
pycharm)
