Fix camera under terrain when exaggeration changes

[astojilj]

Fixes issues when camera center would not change altitude if exaggeration changed and that camera could appear under terrain.

Changelog:

Fixes issues where camera appears under terrain, or map gets bumpy repositioning when exaggeration changes.

Similar to #11461, the customer was affected (https://github.com/mapbox/mapbox-maps-android-internal/issues/850) by camera moved underground when animating exaggeration, increasing it from 0. In such use case, we didn't adjust center and camera MSL altitude with exaggeration change.

There is a chance that previous behavior, that is anchoring camera center to sea level while terrain elevates, is desired. However, it is not productized and not feasible in high altitude areas (e.g. camera positioned over Denver would quickly go underground when changing exaggeration 0 -> 0.5). There's also issue with position of e.g. markers noticeable on the capture (before, under terrain at the end of video):

before.mov

The change aligns the behavior to existing terrain enable / disable: content under center of screen remains under the center of screen at the same distance when terrain is enabled and when exaggeration changes.

Extended usage of Transform._centerAltitudeValid to renamed _centerAltitudeValidForExaggeration: while data is not available, _centerAltitudeValidForExaggeration is 0. As soon as center elevation is available, new value for _centerAltitudeValidForExaggeration would trigger camera altitude adjustment in updateElevation.

Fog demo: change exaggeration by pitch and zoom options
Added exaggeration change on zoom (issue #11044 is still open) and pitch (bug #11589) to fog demo.

Fog change:
There was a flicker when disabling terrain, related to average elevation calculated before terrain update (fog would render during the first frame using high elevation), followed by fog transition animation. Average elevation easing is disabled for camera exaggeration change.

fogtransitionbefore.mov

After fix there is still flicker noticeable when exaggeration changes to 0. This one is related to tile cover missing tiles (fog matrices used in rendering are up to date):

after.mov

Follow up (a separate issue that exists in main branch too):

• marker popup doesn't change position when terrain changes (enabled/disabled or exaggeration change) Marker popup position is not updated when terrain changes #11579

Fixes: #11589

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
• keep existing behavior for drag and zoom
• document any changes to public APIs
• post benchmark scores
• manually test the debug page
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• tagged @mapbox/gl-native if this PR includes shader changes or needs a native port
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• add an entry inside this element for inclusion in the mapbox-gl-js changelog: <changelog></changelog>

[astojilj]

The PR doesn't handle drag and zoom properly (sea elevation reference) when exaggeration changes with zoom

drag.mov

Needs to be resolved within this PR.

Edit:
This exists in main branch too, #11044 (comment) and needs to be fixed later.

[astojilj]

The PR doesn't handle drag and zoom properly (sea elevation reference) when exaggeration changes with zoom

drag.mov
Needs to be resolved within this PR.

This issue exists in main branch too: #11044 (comment) and needs to be fixed later.

Added exaggeration change on pitch (bug #11589) to fog demo can be used to verify that this fixes issue #11589):

fix.mov

[karimnaaji]

This issue exists in main branch too: #11044 (comment) and needs to be fixed later.

Thanks for capturing that issue!