Disable sky after maximum projection transition to mercator

[karimnaaji]

For non-mercator projection, this PR disables the sky layer after the end range of all projections that aren't mercator (as suggested in #11124 (comment)). This ensures that the sky is disabled before the end of sheer adjustment range where projections are set to mercator at high zoom levels.

Fixes #11207

The motivation is to give more thoughts on whether we could use it as a background fill for empty projection space. Some options that we should consider then:

• Use a gl.clear using the background color to fill space where tiles aren't drawn
• Leverage the sky layer below the horizon line for that use case
• Transition to alpha = 0 below the horizon line when a sky is available (as mentioned by @arindam1993)
• Some other options?

Launch Checklist

• briefly describe the changes in this PR
• document any changes to public APIs
• manually test the debug page
• apply changelog label ('bug', 'feature', 'docs', etc) or use the label 'skip changelog'

[arindam1993]

This looks good, but I think we need to add in this
a9ddf15
to prevent this #11207 , cauze there might still be situations where the frustum culling conflicts causing flickering in and out.

[arindam1993]

LGTM otherwise