Windows: Switch UWP build to using winrt generated headers

[clarkezone]

This change switches the Windows UWP build from shipped cppwinrt headers to headers generated by the cppwinrt tool.

• Fix support for the latest Windows SDK (10.0.19041.0) by generating winrt SDK headers from SDK metadata rather than using shipped headers which have clang compatibility bugs. SDK metadata is the source of truth for the WinRT ABI; by using the latest tool rather than shipped headers, most recent compatibility fixes can be picked up on an ongoing basis.

Depends on flutter/buildroot#442

flutter/flutter#70205
flutter/flutter#14967

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[flutter-dashboard]

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[cbracken]

LGTM. Dependent patch flutter/buildroot#442 needs a quick fix then the annotated buildroot roll before landing.

[chinmaygarde]

The dependent patch looks good to me after @clarkezone addressed @cbracken s comments on it. I believe this patch is unblocked. Lets land it soon (after fixing the DEPS entry of course 😄 )

[clarkezone]

Thx, I'll land both this evening

[cbracken]

Kicked build_and_test_linux_unopt_debug. Re-run: https://cirrus-ci.com/task/4666251248140288. Flake report filed.

[cbracken]

Looks like it hung on ShellTest.SkipAndSubmitFrame.

[ RUN      ] ShellTest.SkipAndSubmitFrame
[FATAL:flutter/testing/test_timeout_listener.cc(45)] Check failed: delay < timeout_. Test ShellTest.SkipAndSubmitFrame did not complete in 30 seconds and is assumed to be hung. Killing the test harness.

Filed another flake.