Support using PlatformColor for designTokens

[ethanshar]

Description

I added support for reading native colors using RN PlatfomColor API for loaded design tokens.
This will only work when the user purposely enable this feature by calling Colors.enabledPlatformColors
The reason for that is that the users must load the relevant colors in their native code.

For now, this will be false in the public code.
We will enable this and load the platform colors in native only in private for now.

Unfortunately, PlatformColor API is not so flexible, for instance I can't try/catch it and return the original JS color, like this

try {
  return PlatformColor('$myToken');
} catch (error) {
  return actualTokenValue;
}

Changelog

Support using RN PlatformColor API for loaded design tokens

[ethanshar]

@Inbal-Tish @M-i-k-e-l @lidord-wix
Please review (and approve), don't merge

[lidord-wix]

It'll open the dark mode to the community before we ready

[zuhair-naqvi]

What's outstanding for dark mode? also where can I find docs on designTokens?