[web] Use Button for text buttons

Summary:
Part of ENG-843
Adds a new 'text' variant to Button and uses it instead of plain html elements in:

• settings screen
• retry send button
• user list in thread composer

to keep the web app more consistent.

This diff also fixes visual bugs with retry message:
Before:

After:

Test Plan:
Check if

• settings screen
• retry send button
• user list in thread composer

look and work correctly.

Reviewers: tomek, atul, abosh, ginsu

Reviewed By: atul, ginsu

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D5322