fix: keep maps as single tab focus targets

[himu-gupta]

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Keep the embedded MapView as the first keyboard focus target for the map so forward Tab navigation treats each GoogleMap as one focus stop before moving to the next Compose item.

Tests:

• ./gradlew :maps-compose:compileDebugKotlin :maps-app:compileDebugAndroidTestKotlin
• ./gradlew :maps-app:assembleDebug
• ./gradlew :maps-compose:lintDebug :maps-app:lintDebug
• ./gradlew :maps-app:lintDebug

Fixes #791 🦕