Prefer the more generic exception type as it's possible exceptions
derive from this and not "Exception".
Also use the name 'ex' for exceptions instead of 'e'.
Now the operator is used for both the internal & external editor,
so there is no need for the caller to call this operator only when
the preferences are set.
Add a user preference to set up a custom text editor for editing text
files with the "Edit Source" action in the UI context menu.
- An operator TEXT_OT_jump_to_file_at_point has been added.
- A custom editor can be set in the user preferences.
- A preset has been included for "Visual Studio Code".
- When the editor is not set, use Blender's internal editor.
Ref !108299.
