Reorganize `./Examples` and `./Tests`

[tig]

I'd like to move all examples, including UICatalog into a subdir ./Examples.

And all of the fluent folders need to be moved into /Tests.

[tig]

@tznind Can you do a PR that fixes the Fluent stuff. I'm confused by which folder is which.

The structure should look like this when done, I think:

./Tests
./Tests/TerminalGuiFluentTesting
./Tests/TerminalGuiFluentTesting/(all the infra for the FluentTests).
./Tests/IntegrationTests/FluentTests

[BDisp]

That was already fixed in my PR #3966. TerminalGuiFluentTesting.Xunit folder was removed.