Fix broken localtests

[zadjii-msft]

We've had a number of ignored test failures for a while now. They're all
in the localtests, which we don't run in CI, so we've been ignoring
them. Plus, I thought that they were due to some test failure in the way
they were authored, so we just let them be.

Turns out, most of them worked just fine. Many were probably just
temporary test failures that got fixed with subsequent PRs.

The only one that's truly tricky here is the TryCreateTab test
removal. From what I can tell, that test would create a Tab, but not
attach the TabViewItem to the XAML tree at all. But then after the
test was cleaned up, the tab's _UpdateTitle coroutine would resume,
and it would try to get the Tab from the weak_this. That weak
pointer would now be pointing at random memory, and the get_strong
would crash. However, the test runner would already be in the middle
of some other test, so it would cause a failure in a random test, not
the TryCreateTab test.

So I'm just getting rid of it entirely. The TryInitializePage test is
more comprehensive and does work, so we'll just use that (and
derivatives) to test the creation of tabs.

• Closes TryDuplicateBadTab and TryDuplicateBadPane unit tests are hanging when run locally #5169
• Closes Keybinding warnings are duplicated after #6635  #6949
• Closes Correct TerminalApp.LocalTests failures #7281
• Might conflict with Helix Testing #6992

[miniksa]

Thanks for getting these fixed up so quickly.

[ghost]

Hello @miniksa!

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[miniksa]

@msftbot wait like 5 minutes before merging

[ghost]

Hello @miniksa!

Because you've given me some instructions on how to help merge this pull request, I'll be modifying my merge approach. Here's how I understand your requirements for merging this pull request:

• I won't merge this pull request until after the UTC date Tue, 18 Aug 2020 18:02:26 GMT, which is in 5 minutes

If this doesn't seem right to you, you can tell me to cancel these instructions and use the auto-merge policy that has been configured for this repository. Try telling me "forget everything I just told you".