[DynamicColorMacOS] Downgrade to warning if appearance is nil

[Saadnajmi]

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native-macos 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native-macos 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

Summary

When a user cuts/copies text from a <TextInput> that has it's text color styled using DynamicColorMacOS, we would get a Redbox saying that the current appearance could not be resolved. Looking into it, it seems that at this point in native code, Appkit returns an appearance of NSAppearanceNameSystem, which seems to correspond to the "Any" case of an asset catalog if you were specifying a color that way instead.

While I'm not sure why cutting/copying text gets us in this state, it seems this is a valid state to be in, where the OS doesn't have the current appearance and just reports back a generic one. Let's fall back to the light color (as you would with an asset catalog) with a warning instead of an error.

Changelog

[MACOS] [CHANGED] - Downgrade DynamicColorMacOS error to warning if appearance is nil

Test Plan

Testing in RNTester, we get a yellow box instead of a redbox.