[lib] Introduce getUniversalCommunityRootPermissionsBlob

Summary:
getUniversalCommunityRootPermissionsBlob is going to emulate the way we construct permissions blobs so it's more extendible towards separating permissions included for all roles in both COMMUNITY_ROOT and COMMUNITY_ANNOUNCEMENT_ROOT.

I'm not completetly deleting universalCommunityPermissions in thread-permissions-types.js yet, but I will do that once I land this entire stack + rebase the stack starting at D9493, since otherwise it'll cause a ton of merge conflicts and broken unit tests.

The rest of this stack will update usages of universalCommunityPermissions besides the unit test with this new method.

Addressess ENG-5761

Depends on D9514

Test Plan:

• Created a community root on both master and this diff stack. Compared the MariaDB JSON blobs for Members permissions
• Created a community announcement root on both master and this diff stack. Compared the MariaDB JSON blobs for Members permissions

In both cases, the JSON was identical

Reviewers: atul, ginsu, ashoat

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D9897