GIDTokenClaim Implementation + Unit Tests #835

Job	Run time
spm-build-test (macos-15, macosx)	1m 30s
spm-build-test (macos-15, iphonesimulator)	2m 36s
pod-lib-lint (macos-13, GoogleSignIn.podspec, --use-static-frameworks)	10m 3s
pod-lib-lint (macos-13, GoogleSignIn.podspec)	14m 53s
pod-lib-lint (macos-13, GoogleSignInSwiftSupport.podspec)	12m 19s
pod-lib-lint (macos-13, GoogleSignInSwiftSupport.podspec, --use-static-frameworks)	12m 36s
	53m 57s

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