UI: Add a custom text editor preference

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.

scripts/presets/text_editor/visual_studio_code.py

@@ -0,0 +1,12 @@
+import bpy
+import platform
+
+filepaths = bpy.context.preferences.filepaths
+
+filepaths.text_editor_args = "-g $filepath:$line:$column"
+
+match platform.system():
+    case "Windows":
+        filepaths.text_editor = "code.cmd"
+    case _:
+        filepaths.text_editor = "code"