Update BlazorWebView Device Tests to have longer timesouts and more retries

[Eilon]

This change was motivated by some flakiness in BlazorWebView tests. The tests fail sometimes, but pass on rerun. And there are no customer reports of these particular errors either.

Example failure: https://dev.azure.com/xamarin/public/_build/results?buildId=111379&view=ms.vss-test-web.build-test-results-tab&runId=2634804&resultId=100000&paneView=debug

With this test output:

System.Exception : Waited 7500ms but couldn't get CoreWebView2.DOMContentLoaded to complete.
   at Microsoft.Maui.MauiBlazorWebView.DeviceTests.WebViewHelpers.WaitForWebViewReady(WebView2 wv2) in D:\a\1\s\src\BlazorWebView\tests\MauiDeviceTests\WebViewHelpers.Windows.cs:line 53
   at Microsoft.Maui.MauiBlazorWebView.DeviceTests.Elements.BlazorWebViewTests.<>c__DisplayClass2_0.<<BlazorWebViewUsesStartPath>b__1>d.MoveNext() in D:\a\1\s\src\BlazorWebView\tests\MauiDeviceTests\Elements\BlazorWebViewTests.cs:line 131
--- End of stack trace from previous location ---
   at Microsoft.Maui.Dispatching.DispatcherExtensions.<>c__DisplayClass3_0.<<DispatchAsync>b__0>d.MoveNext() in D:\a\1\s\src\Core\src\Dispatching\DispatcherExtensions.cs:line 88
--- End of stack trace from previous location ---
   at Microsoft.Maui.Dispatching.DispatcherExtensions.<>c__DisplayClass2_0`1.<<DispatchAsync>b__0>d.MoveNext() in D:\a\1\s\src\Core\src\Dispatching\DispatcherExtensions.cs:line 67
--- End of stack trace from previous location ---
   at Microsoft.Maui.MauiBlazorWebView.DeviceTests.Elements.BlazorWebViewTests.BlazorWebViewUsesStartPath() in D:\a\1\s\src\BlazorWebView\tests\MauiDeviceTests\Elements\BlazorWebViewTests.cs:line 127
--- End of stack trace from previous location ---

There are a few parts to this change:

1. Increase retries and timeouts of all BlazorWebView tests.
2. Fix place where there was no retry at all
3. Change the BlazorWebView tests to use the same HandleTestBase classes used in other control tests. For some reason the tests would run fine on CI, but fail on my machine due to some service not being registered. No idea how that's possible. But the base test classes used in these tests got very out-of-date compared to other tests, so this brings them inline with other tests.
   • Why not use the actual same base classes? For now that's a lot more work because the Blazor test project can't reference the Controls test project without causing problems (it's not a regular ClassLib). And moving the classes to a new shared library is a lot more work. And the Blazor tests don't need much to begin with (I deleted a lot of unused code from the copy).
4. Small change to the test base classes to be compatible with the async disposal needed by BlazorWebView tests. This is a superset of what was being done before (async disposal also calls sync disposal)

[Eilon]

The retries are now consistently 30 retries * 1000ms.

[Eilon]

This code here never had a retry (despite the exception message saying it did!). And this is where the test failure that motivated this change occured - so hopefully adding retries mitigates that particular flakiness.

[Eilon]

MAUI team reviewers: This is the part of the change that can affect other tests: I changed this to be IAsyncDisposable (which the BlazorWebView tests always did). In theory this is a good change anyway because MauiApp is IAsyncDisposable so should really always be disposed that way.

[Eilon]

(This was never needed because the base class already declared its disposableness.)

[Eilon]

This file and the next few files (AppStub, ControlHandlerTestBase, etc.) are copied from the MAUI Controls DeviceTests, but I then removed anything that wasn't needed by the BlazorWebView tests (it was too hard to get it to compile, and too hard to directly reuse the types).

[Eilon]

@ruiminhu / @PureWeen - can one of you do a tiny review for the small changes to the DeviceTests base handler types? (I put comments in the PR to explain everything).

@dotnet/dotnet-maui-blazor-eng - anyone available to review my BlazorWebView test changes? There's a lot of code shuffling but the core change is simply to add more retries to some test segments that have failed on CI (but always pass on rerun 😠 ).