[native] Add markdownASTHasPressable to TextMessageMarkdownContext

Summary: We need to know whether the Markdown has any pressables because we're going to render it differently in that case.

Test Plan:
I tested the following text and made sure each link counted as pressable:

Here’s a [link](https://comm.app)

Here’s a **bold [link2](https://comm.app)**

here’s a [**bold link3**](https://comm.app)

Here’s a raw link https://comm.app

Here’s a **bolded raw link https://comm.app**

Reviewers: rohan, atul, ginsu, michal

Reviewed By: rohan, atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D5755