All Mac builders in both framework and devicelab need to use xcode 12.3 which includes swift

[keyonghan]

Most of Mac builders are using an old xcode version 11.3, which misses swift dependency. This causes intermittent problems like:
#73606
#72823

Per discussions https://github.com/flutter/infra/pull/325, we need update all builders to use latest xcode 12.3.

[godofredoc]

Closing as obsolete.

[github-actions]

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