Mapbox: Dummy map impl with the required fallback values.

[quimodotcom]

Fixes: #3549

Changes:

• Implemented hasAnyMapKey() to detect missing or placeholder API keys.
• Implemented DummyGoogleMapImpl and associated dummy delegates to gracefully handle map operations without the native library.
• Integrated the dummy implementation into MapViewImpl and MapFragmentImpl.
• Provided an empty style JSON fallback in Styles.kt.