WIP: Fix nested text styling not inheriting from parent

[rayan1810]

This addresses the issue #4351 by adding a React Context with Text Component and checks + reads the parent Text's context to get it's style and merges it with the current Text's style, just like how React Native behaves.

Related issue

#4351

Test plan

Testing is pending, the PR is still a Work in progress!

[callstack-bot]

Hey @rayan1810, thank you for your pull request 🤗. The documentation from this branch can be viewed here.

[scarletcs]

It seems to me as though this will overwrite any element-specific styling with the parent styling, such that this would output both words in blue:

<Text style={{color: "blue"}}>
  Blue!
  <Text style={{color: "red"}}>
    Red!
  </Text>
</Text>

So the following code would be preferable instead:

if (parentTextContext) {
  textStyle = Object.assign(StyleSheet.flatten(parentTextContext.style), textStyle);
}