[lib] Introduce a canBeSidebarSource function in each message spec

Summary:
The last part of unifying the logic and source of truth for determining eligible messages to be sidebar sources is to have a canBeSidebarSource function in each message spec. This diff introduces the constant to each existing message spec, and the next diffs will replace the logic in to isInvalidSidebarSoruce to call the message spec. This ensures that we'll only ever need to update the specific message spec in one place and the ValidRawSidebarSourceMessageInfo type if we ever want to change this.

Depends on D9324

Resolves https://linear.app/comm/issue/ENG-5208/introduce-a-canbesidebarsource-function-in-each-message-spec

Test Plan: Ran flow and updated the unit tests to call canBeSidebarSource. yarn workspace lib test passes all tests

Reviewers: atul, ginsu

Reviewed By: ginsu

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D9325