Fix blurry map-aligned labels on terrain

[mourner]

Closes #10220. Before we added terrain, we had a heuristic for map-aligned labels to get blurrier as you pitch the map to compensate for aliasing when labels get squished. However, this approach breaks on terrain-enabled maps because we can't adjust all labels equally — some of them will be on hilly areas and not as squished, as apparent in the issue.

This is an easy fix that simply disables map-alignment label blurring when on terrain. Ideally, in future we could reintroduce this blurring properly by moving from a global gamma adjustment to one calculated in the vertex shader depending on the slope, but that's too involved for the small benefit at the moment — labels look pretty good on terrain with this fix too.

Before:

After:

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
• manually test the debug page
• tagged @astojilj because this affects native port
• apply changelog label ('bug', 'feature', 'docs', etc) or use the label 'skip changelog'
• add an entry inside this element for inclusion in the mapbox-gl-js changelog: <changelog>Fix blurry map-aligned labels on highly pitched maps with terrain</changelog>