Implement <MarkdownText /> (Native only)

[s77rt]

This PR is for implementing <MarkdownText /> on native. The web version will be handled separately later on.

[s77rt]

TODO:

• Check s77rt comments

[s77rt]

I'm already facing issues with iOS, the attributed text is of type AttributedString and not NSAttributedString this means we can't apply our attributes as they are meant to work with the later.

Possible solutions:

• Work with a new NSAttributedString then convert it to AttributedString. This is probably the best option but I don't know if the conversion is possible, react core currently does not offer such an utility, maybe we can wait to see if this changes.
• Work with AttributedString and write new parser that works with its attributes. Not really a fan of this idea as it creates more work and we will have to get rid of the other parser and only use AttributedString.
• Override the drawRect method and write our own drawer that takes a NSAttributedString directly (after all, the AttributedString is converted to NSAttributedString in the end). I think this is easy to do but we will have to copy some logic from react core which I don't really like as it will require maintenance.