Show a user's display name for 'is typing' indicator

[Jag96]

@NikkiWines will you please review this?

Details

This PR adds a check for the displayName inside getDisplayName, since we can set that value inside formatPersonalDetails but not set the first/last name. I've also added the first/last name to formatPersonalDetails to ensure that when we fetch the personalDetailsList, we're storing those values in Onyx. If there is a reason we don't want to do this, please let me know, but since we're using first/last name in other parts of the app it made sense to add it here.

Fixed Issues

Fixes Expensify/Expensify/issues/159835

Tests

1. Login as User A who has personal details set for first and last name (you can set these values by clicking on the profile icon, then clicking on profile)
2. Login as User B and start a chat with User A
3. Type in the textbox as User A, see that User A's first and last name show up instead of their email address
4. For a user who does not have first/last name set, type as that user and confirm that in the opposite chat window the email address still shows

I also confirmed the following works

1. User A types, User B sees personalDetail name
2. User A changes name, User A sees personalDetail name updated everywhere
3. User A types, User B sees old name in "is typing" indicator
4. User B refreshes
5. User A types after refresh, "Is typing" indicator shows User A's new name

QA Steps

1. Login as User A who has personal details set for first and last name (you can set these values by clicking on the profile icon, then clicking on profile)
2. Login as User B and start a chat with User A
3. Type in the textbox as User A, see that User A's first and last name show up instead of their email address

Note: a regression is being added for this in https://github.com/Expensify/Expensify/issues/159794

Tested On

• Web
• Mobile Web
• Desktop
• iOS
• Android

Screenshots

[NikkiWines]

Looks good, one comment about the re-introduction of userDetails.displayName

[Jag96]

OK, #2317 (comment) is sorted, this is ready for another review

[NikkiWines]

Works well!!

[Jag96]

Updated!

[NikkiWines]

[MariaHCD]

LGTM!