Build visual tree compare tests that iterate over RNTester pages

[chrisglein]

@ddalp built out some visual tree comparison test infrastructure recently: #3754
We're going to use that more as we do new feature work, but we have a lot of test debt in everything we built before we had this or the general E2E test infrastructure. One thing we can do is take the existing content in RNTester and enumerate over it, grabbing a visual tree dump as we go. Even if it's just static (no interaction with the page), that's test coverage we don't have. Seems like a good way to bolster our test coverage.

Note that not all of the RNTester pages are testing ViewManagers. We should limit this task to only the RNTester pages that cover ViewManagers and their properties.

List of ViewManagers we want to cover - examples files in brackets:

Higher Priority / In Progress

• Button
• FlyoutVM (FlyoutExample)
• ImageVM (ImageExample)
• PopupVM (PopupExample)
• ScrollVM (several pages: eg. ScrollViewExample)
• SwitchVM (switchexample)
• TextInputVM (textinputexample)
• TextVM, VirtualTextVM, RawTextVM (textexample)
• ViewVM
• Pressable

Lower Priority

• ActivityIndicatorVM (activityindicatorExample)
• FrameworkElemVM
• GlyphVM (GlyphExample)
• RefreshControlManager (refreshcontrolexample)
• RootVM