Fix flaky AppTile tests

[Half-Shot]

Fixes #31439

This is a really fiddly test, but have tried to break it down so it now works:

• We only call render( inside the it blocks, as otherwise it's hard to tell the ordering of the various nested beforeEach calls.
• We had places where state was not being reset between tests such as Settings and Widget stores.
• I removed logger.log("returning theme value"); as it was driving me crazy and providing little value.

[robintown]

Nice, having these tests wait for the loading indicator to be gone looks a lot safer.