[core] Locally generated glyphs shift on over-zoomed tiles

[chloekraw]

GL-Native version of mapbox/mapbox-gl-js#8653

@asheemmamoowala @mapbox/gl-native @tmpsantos

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When zooming from z17 to z18, some locally generated glyphs are being replaced by server retrieved glyphs.

On z18 tiles, the glyphs have variable size which is a property of the server generated glyphs. The z17 tiles have fixed size (24/32 px sq.) size that is characteristic of locally generated glyphs.

platform: iOS and Android
version: 5.2 / 8.2

Demonstration

GIF created from an iOS screen recording:

Also see mapbox/mapbox-gl-js#8653 for helpful visuals on GL-JS.

Expected Behavior

Locally generated glyphs are not overridden by server generated ones.

Actual Behavior

At z18 server glyphs are taking over. Causing a change in the baseline and font of some characters.

[chloekraw]

@asheemmamoowala I noticed your native pr #15407 is slimmer than your js pr mapbox/mapbox-gl-js#8657. Is that because some changes on js are not needed in native, or because #15407 is what we can get into queso and other changes could be done as follow-on work for ristretto?

[asheemmamoowala]

@chloekraw I found two additional issues while debugging the root cause of this bug on GL-JS and decide to address them as well. On Native, the local glyphs are already being cached correctly. I haven't yet had a chance to verify the other issue - correct options override in Map#setStyle, but I'll look into it as part of completing the tests for this PR.