[native] introduce userProfileBottomSheetActive state to markdown context

Summary:
In order to block focusing a text message whenever an @mention of a user is pressed, we need to introduce a piece of state called userProfileBottomSheetActive to the markdown context provider. We need to block focusing a text message, because otherwise this will block the navigation to the user profile, which is not what we want

This is step 3 in the list below
Outlined below are the steps I will take to make @metion of a user into a touchable

1. Introduce createMemberMapForUserMentions function (Right now we only store a set of usernames but we also will want to know the id of the user based on the username)
2. Introduce parseUserMentions function (We will use this function to get and return a userID from the membersMap)
3. Introduce userProfileBottomSheetActive state to the markdown context (This will be used for disabling the press to focus on a message functionality)
4. Introduce MarkdownUserMention component (this will render the touchable that will navigate to the user profile)

Depends on D9392

Test Plan: Logged out the value of isUserProfileActive in the TextMessage component, and confirmed that I confirmed that I was getting a false value (which is to be expected), and also confirmed that I could make calls to setIsUserProfileActive

Reviewers: atul, inka

Reviewed By: atul

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9393