fix: avoid zero-size crash in rememberComposeBitmapDescriptor when used inside Clustering - #963

Summary

• rememberComposeBitmapDescriptor hosted its throwaway rendering ComposeView on LocalView.current, which can itself be mid-attach with no Android layout pass performed on it yet — this happens when the function is called from content composed inside Clustering's clusterItemContent, since the InvalidatingComposeView hosting that content is still being attached to its own parent at that exact point. measure() returned a 0x0 size and the function threw IllegalStateException.
• Fix hosts the throwaway view on the window's root view instead, which is already laid out by the time any marker/cluster content is composed. setParentCompositionContext keeps the composition correctly scoped to the caller regardless of which Android View it's physically parented under, so this is safe.
• Note: this fixes rememberComposeBitmapDescriptor itself. Nesting the full MarkerComposable (not just rememberComposeBitmapDescriptor) inside Clustering's clusterItemContent is a separate, unsupported combination — MarkerComposable also places a Marker node via MapApplier, which doesn't exist in that composition context, and will still throw IllegalStateException: Invalid applier regardless of this fix.

Fixes #694

Test plan

• Added testClusterItemContentUsingRememberComposeBitmapDescriptorDoesNotCrash to GoogleMapViewClusteringTests, calling rememberComposeBitmapDescriptor from inside clusterItemContent — reproduces the crash pre-fix, passes post-fix.
• Ran GoogleMapViewClusteringTests on a physical device (Pixel 4, API 33): all 3 tests pass.
• Manually reproduced the original crash on-device (IllegalStateException: The ComposeView was measured to have a width or height of zero) and confirmed it no longer occurs after the fix.