Fix Adreno GPU crashes from symbol UBO dynamic indexing

[navidemad]

Summary

Fixes #13651 — v3.21.0 crashes on Android Pixel devices (Pixel 7, 8, 8A, 9a) during zoom/pan due to Adreno GPU incompatibility with the new symbol UBO feature.

Root cause: Adreno GPUs (like PowerVR, already disabled in 9880b06b4) do not correctly handle dynamic (non-uniform) indexing into UBO arrays — this is technically undefined behavior in GLSL ES 3.00. The symbol shader also had inconsistent Adreno workarounds: uvec4At/vec4At used safe explicit swizzles, but readFloat/readUint used direct bracket indexing that fails on affected Adreno drivers.

Changes:

• src/gl/context.ts — Disable symbol UBO batching on Adreno GPUs (matching the existing PowerVR treatment)
• src/shaders/symbol.vertex.glsl — Replace direct slot[index] bracket indexing in readFloat/readUint with the existing Adreno-safe vec4At/uvec4At helpers
• src/data/bucket/symbol_properties_ubo.ts — Fix stale default parameter in getMaxFeatureCount (was 4096 - 12 = 4084, should be 4096 after the sizing fix in e56c56731)
• src/render/cutoff.ts — Guard zRange division against near-zero values on mobile viewports

Test plan

• symbol_property_binder_ubo.test.ts — all 35 tests pass
• Verify on Pixel 7/8/8A/9a that zoom/pan no longer crashes
• Verify on desktop that symbol rendering is unchanged (UBO still active on non-Adreno/non-PowerVR GPUs)
• Verify on PowerVR devices that existing disable still works

🤖 Generated with Claude Code

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[navidemad]

Closing in favor of a new PR rebased onto main with changelog entry added per CONTRIBUTING.md.