Update support table; run readthedocs build on Python 3.11

Author: mhsmith

Diff for: .readthedocs.yaml

@@ -7,7 +7,9 @@ version: 2
 build:
   os: ubuntu-22.04
   tools:
-    python: "3"
+    # On Python 3.12, pip fails with AttributeError: module 'pkgutil' has no attribute
+    # 'ImpImporter', probably because readthedocs provides an old version of pip.
+    python: "3.11"
   jobs:
     post_checkout:
       # RTD defaults to a depth of 50 but Toga versioning may require

Diff for: docs/reference/data/widgets_by_platform.csv

@@ -1,7 +1,7 @@
 Component,Type,Component,Description,macOS,GTK,Windows,iOS,Android,Web,Terminal
 Application,Core Component,:class:`~toga.App`,The application itself,|b|,|b|,|b|,|b|,|b|,|b|,|b|
-Window,Core Component,:class:`~toga.Window`,An operating system-managed container of widgets.,|b|,|b|,|b|,|b|,|b|,|b|,|b|
-MainWindow,Core Component,:class:`~toga.MainWindow`,The main window of the application.,|b|,|b|,|b|,|b|,|b|,|b|,|b|
+Window,Core Component,:class:`~toga.Window`,An operating system-managed container of widgets.,|y|,|y|,|y|,|y|,|y|,|b|,|b|
+MainWindow,Core Component,:class:`~toga.MainWindow`,The main window of the application.,|y|,|y|,|y|,|y|,|y|,|b|,|b|
 ActivityIndicator,General Widget,:class:`~toga.ActivityIndicator`,A spinning activity animation,|y|,|y|,,,,|b|,
 Button,General Widget,:class:`~toga.Button`,Basic clickable Button,|y|,|y|,|y|,|y|,|y|,|b|,|b|
 Canvas,General Widget,:class:`~toga.Canvas`,A drawing area for 2D vector graphics.,|y|,|y|,|y|,|y|,|y|,,