Crashlytics watchOS support

[jostster]

This PR resolves #4558 and adds crashlytics support for watchOS 6.0 +

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[jostster]

@googlebot I signed it!

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[paulb777]

This is great! Thanks!

Please add to CI by updating https://github.com/firebase/firebase-ios-sdk/blob/master/.github/workflows/crashlytics.yml.

Since XCTest is not supported it should be:

target: [ios, tvos, macos, watchos --skip-tests].

See also GHA change in #6260

[paulb777]

LGTM - #6263 should address the travis failure.

Deferring to @samedson for approval and merge

[samedson]

Congrats on this! Thanks for making it happen!

[jostster]

@samedson looks like one check failed and was because of teamid during the build. I assume that is fine?

[paulb777]

@jostster That build failure is addressed by #6263. I'll merge this one here. Thanks!