Documenting differences between RNW and RN Win32

[rurikoaraki]

Opening this issue to collect documentation of areas that are forked or have different behaviors between RNW and RNWin32. As RN Win32 turns toward aligning with RNW, we want to make sure that we are addressing any functionality differences or gaps that we will encounter.

• enableFocusRing default behavior (false for win32 and true for windows).
• ImageLoader.getSize uses a callback instead of a promise in win32
• Accessibility gaps probably exist (i.e. accessibilityAccessKey)

@acoates-ms FYI

[rurikoaraki]

Accessibility gaps probably exist (i.e. accessibilityAccessKey)

[rurikoaraki]

enableFocusRing default behavior (false for win32 and true for windows). No technical reason for this one, mostly for staging the additional behavior.

[chrisglein]

Expectation is that the documentation occurs here (in the issue) with tasklists or whatever. Wiki is fine too. @Khalef1 assigning to you until you have someone designated.

[rurikoaraki]

Possible fork in behavior for keyboard focus in context menus.