Improve settings editor accessibility

[9at8]

#97567

This PR includes a number of improvements in the settings editor.

Settings is made up of smaller virtual lists for each category

Each group only renders its own settings, and scrolling the settings list doesn't cross into a different group. The current settings editor is just one giant list of all settings. This change makes the settings page easier to navigate, and also make it less intimidating.

Before	After

Settings are navigable using arrow keys instead of tab keys

This change makes navigating the settings editor experience closer to what it's like for lists and trees in other parts of VSCode. Before, the setting page behaved like a form. That is, users had to tab through each control on the page to navigate to a setting. Now, users can tab to the settings list once and then use arrow keys to jump from one setting to the next. To edit that setting, they can press the tab key to go into the settings control.

Before	After

TOC tree can be focused by pressing Escape while navigating the settings list

Before, there was no easy way to focus on the table of contents on the left. Now, users can press the Escape key while focused on a setting to jump to the table of contents. Pressing escape again shifts focus back to the search box!

Before	After

[9at8]

cc: @roblourens