SUI Nullable Colors & Icon control Follow-ups

[carlos-zamora]

Follow-ups from #17870:

• [A11y] Screen readers don't read expander's preview text
  • Tracked in Expander Header not read by screen reader if it's complex microsoft-ui-xaml#10282
  • Hmm... it might be better to just directly set the AutomationProperty.Name
  • PR Make SUI previews readable by screen readers #18418
• Add Tab Color to settings UI
  • PR Add tab color setting to settings UI #19351
• Update CursorColor preview to display #FFFFFF as "invert"
• Use Leonard's font picker UI, with the Segoe icon picker, so that you can filter the list
  • PR Replace BuiltInIcon ComboBox with AutoSuggestBox #19569
• [High contrast] we should probably add borders to the color chip previews

From Bug bash 1/21

• [Windows 10] Conflicting Windows & app theme causes this:
  

• [Windows 10] Checkmark icon is missing!
  

• Narrow window = cut off
  

• When using an emoji for the Profile icon, I run into this while using certain emojis (shield) though that might just be an issue with the emoji itself (not our problem?)