Generate build & test matrix from script

[sunmou99]

Description

Generate build & test matrix from script:
build matrix format: unity_version-build_os-platform-ios_sdk
test matrix format: unity_version-build_os-platform-test_device-test_os

Updated some configs.

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Testing

Build & Test against one testapp: https://github.com/firebase/firebase-unity-sdk/actions/runs/3276829085

Also, see comment below

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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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