Add architectures to desktop integration test matrix, and enable arm64/x86 tests.

[jonsimantov]

Description

Provide details of the change, and generalize the change in the PR title above.

Add arch to the build_desktop matrix, and add architecture tags to all of the artifact names etc.

This allows us to:

• Actually use the architecture_* fields in print_matrix_configuration.py
• Enable arm64 Mac tests on our M1 Mac GitHub custom runner (when testing on the expanded matrix).
• Enable x86 Linux/Windows tests (when testing on the expanded matrix).
  • For Linux, this required moving the x86 runner setup to a shared module and add customization options to the install prereqs script.

This PR includes all of the above. And look, it reveals some bugs! e.g. an x86 issue in RTDB (fixed in #939)

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Testing

Describe how you've tested these changes. Link any manually triggered Integration tests or CPP binary SDK Packaging Github Action workflows, if applicable.

Full integration test run on this PR.
Integration test on packaged SDK here.

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Type of Change

Place an x the applicable box:

• Bug fix. Add the issue # below if applicable.
• New feature. A non-breaking change which adds functionality.
• Other, such as a build process or documentation change.

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Notes

• Bug fixes and feature changes require an update to the Release Notes section of release_build_files/readme.md.
• Read the contribution guidelines CONTRIBUTING.md.
• Changes to the public API require an internal API review. If you'd like to help us make Firebase APIs better, please propose your change in a feature request so that we can discuss it together.

[github-actions]

Integration test with FLAKINESS (succeeded after retry)

Requested by @jonsimantov on commit 1d1bba1
Last updated: Tue May 10 00:18 PDT 2022
View integration test log & download artifacts

Failures	Configs
firestore	[TEST] [FLAKINESS] [Android] [1/2 os: macos] [android_target] (1 failed tests)   ServerTimestampTest.TestServerTimestampsUsesPreviousValueFromLocalMutation

Add flaky tests to go/fpl-cpp-flake-tracker