Make SUI previews readable by screen readers

[carlos-zamora]

Summary of the Pull Request

Fixes a few accessibility bugs in the SettingContainer previews. Main changes include:

• SettingContainer was considered a separate UIA element from the inner expander. It's been marked as AccessibilityView=Raw to "remove" it from the UIA tree.
• Added a CurrentValueAccessibleName property to the SettingContainer to expose the current value to the screen reader for SettingContainers that have expanders. Non-expander SetttingContainers already worked fine.
• Applied CurrentValueAccessibleName to various settings throughout the settings UI for full coverage. Added a CurrentValue for the ones that were missing it.
• Removed a redundant/hidden tab stop in Icon

References and Relevant Issues

Padding was not updated since #18300 is handling that. This'll just automatically make it accessible.
Font axes and features weren't updated to show previews, but I'm happy to do it if given a suggestion.

Part of #18318

Detailed Description of the Pull Request / Additional comments

• SettingContainer updates:
  • AccessibilityView = Raw for SettingContainers with expanders. This is because the expander itself is the one we care about. No need to have another layer of UIA objects saying it's a group.
  • Added a CurrentValueAccessibleName property
    • This specifically defines what should be read out by the screen reader, similar to AutomationProperties.Name
    • It updates automatically when CurrentValue changes.
    • It's applied on the inner Expander, if one exists.
    • The accessible name is constructed to be "<Header>: <CurrentValueAccessibleName>". If CurrentValueAccessibleName isn't provided, we try to use the CurrentValue if it's a string.
• Profile (and appearance) settings:
  • Icon's value is now read out by a screen reader instead of staying silent. It'll read the icon path.
  • A redundant/hidden tab stop was removed from Icon.
  • TabTitle now displays/reads "None" if no tab title is set.
  • ColorScheme is now read out by a screen reader.
  • The color scheme overrides (i.e. Foreground, Background, SelectionBackground, and CursorColor) are now read out by a screen reader. Format is "#".
  • BackgroundImageAlignment is now displayed and read out by a screen reader.
• LaunchSize is now displayed and read out by a screen reader. Format is "Width x Height".

Validation Steps Performed

Tabbed through the settings UI with a screen reader. Each of these settings now reads out a preview.