[tests] Better support running on arm64-v8a devices

[pjcollins]

MSBuild device tests that specified a subset of supported ABIs can fail
depending on your target device/emulator. These tests have been updated
to use the default ABI of the attached device, which is determined
during test setup.

Tests which explicitly specify the full set of supported ABIs have been
left unchanged.

[dellis1972]

Looks ok.
I do wonder if we need to make sure we have at least one test which runs an app which does have a full set of abis? The reasoning is to make sure we do not break abi detection in the fast dev process.

[pjcollins]

Looks ok. I do wonder if we need to make sure we have at least one test which runs an app which does have a full set of abis? The reasoning is to make sure we do not break abi detection in the fast dev process.

We do still have a dozen tests or so in InstallAndRunTests and other classes that were explicitly setting support for all ABIs, I left those unchanged. We also have tests that don't modify the property at all.

We could also try to remove many of these supported ABI overrides now that main is .NET only, as our defaults there for both debug and release are more extensive.