Add Android.mk to the new fabric template

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Feature request

It would be nice to have a fabric template with Android.mk

Why it is needed

Fabric was introduced at react-native@0.68, and full CMake support was introduced at react-native@0.71

We are working on fabric packages for 0.69 and need fabric template with Android.mk

Possible implementation

• Android.mk in app template of react-native@0.69.8
• Android.mk in app template of react-native@0.68.6
• Android.mk in library code of react-native-safe-area-context@v4.3.1 & react-native@0.69.0-rc.6

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In case someone interested, here is a backport PR: Backport fabric-compat/fabric-only android to react-native@0.68/0.69

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Note: Breaking: Remove androidMkPath from react-native config

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Here is the PR Backport androidmk for react-native-builder-bob