[TabContextMenu] Set up TabContextMenuCoordinator and test file

This also involved renaming IDS_TAB_GRID_DIALOG_REMOVE_FROM_GROUP to IDS_REMOVE_TAB_FROM_GROUP (making it more generic), which required changes in TabGridDialogMediator & test.

Bug: 397247439
Test: TabContextMenuCoordinatorUnitTest
Change-Id: I0e2cf4ea0becc7b9524887a6d5e956d554693f78
Low-Coverage-Reason: This initial CL sets up the coordinator class, test file, and ids. Most of the added code is not yet utilized in this CL due to pending implementations. Test cases will be added in subsequent CLs as the implementations are added.
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6289174
Commit-Queue: Jenna Himawan <jhimawan@google.com>
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Reviewed-by: Neil Coronado <nemco@google.com>
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1424128}