Ensure tile mask geometry buffers are cleared when tile is unloaded

[arindam1993]

Clear tile mask buffers when tiles are unloaded.
Cherrypick of the fix for the memory leak from #8814 .

Launch Checklist

• briefly describe the changes in this PR
• include before/after visuals or gifs if this PR includes visual changes
• write tests for all new functionality
• document any changes to public APIs
• post benchmark scores
• manually test the debug page
• tagged @mapbox/studio and/or @mapbox/maps-design if this PR includes style spec or visual changes
• tagged @mapbox/gl-native if this PR includes shader changes or needs a native port

[asheemmamoowala]

@arindam1993 What's the best way to verify these changes?

[arindam1993]

@arindam1993 What's the best way to verify these changes?

I used the instrumented gl calls similar to #8814, and did a manual check on if the object count so see if it flattened out. But did not include that in this PR. Should I move the modified test page over as well?

I think an extension to the gl-stats page with a longer running test that plots growth over time would be a more formal way to check for things like this.