[lib] Extract action types constants out of socket-types.js

Summary:
In a later diff, we end up with an import cycle after adding an action type constant to this file and importing it from CallKeyserverEndpointProvider.

To avoid that import cycle, I decided to move the action types in this file to another file. I then modified the following diff to define the new action type constant in the new file.

Depends on D10946

Test Plan:

1. Test successful session invalidation in single keyserver world
   1. I prevented the Socket from rendering by adding a return null line before the other returns in KeyserverConnectionHandler. This avoided the Socket triggering session recovery.
   2. I started the iOS simulator and logged in using a test user.
   3. I opened the Redux Dev Tools
   4. I deleted the test user's cookie from the MariaDB database: DELETE FROM cookies WHERE user = 6390578 AND platform = 'ios'
   5. I sent a message as the test user
   6. I confirmed that session recovery was triggered in the Redux dev tools (and through some console logs)
   7. I repeated the process above several times to make sure it consistently worked multiple times in a single run
   8. I confirmed that the message was delivered "transparently" (without any visible issues, or evidence of session invalidation)
2. Test failed session invalidation in single keyserver world
   1. I ran through the above test, but I hacked legacy-recover-keyserver-session.js to use the wrong password so the session recovery would fail
   2. I confirmed that I was logged out, and that an alert appeared explaining that my session was invalidated
3. Test logging out during session recovery
   1. I triggered an infinite loop of session recoveries by running through the above test, but swallowing the SET_NEW_SESSION
   2. I logged out of the app
   3. I confirmed that the session recovery loop stopped, and that I was logged out successfully

Reviewers: tomek, inka

Reviewed By: inka

Differential Revision: https://phab.comm.dev/D10947