* Extract `ignore` util to separate header.
* `Segment` now tracks offset and length of indices, rather than primitives. This is more natural.
* Introduce `VertexVector` and `IndexVector` types. These types carry information about the intended draw mode (`Triangles`, `LineStrip`, etc.), and ensure that elements are always appended in a group size appropriate for that draw mode, for both indexed and unindexed rendering.
* `Program`, rather than `Drawable`, is now the unifying object for draw calls. `Program` is the best place to type check the draw call, because it is typed to carry information about the intended primitive, vertex type, attributes, and uniforms.
* Use the debug shaders for debug tile rendering, like gl-js.
* Fix the draw mode for background. It was drawing triangle strips with a triangles array. Surprised this didn’t cause issues. Now it’s type checked.
Template on shader types, rather than count. This allows the compiler to enforce using the correct VAO for the shader and PaintMode. This fixes OverdrawMode with circle layers.
While here, avoid using unique_ptrs for groups. Instead, ensure ElementGroup is movable.
SymbolLayout lives on the worker thread and contains the persistent data needed for repeated placement. SymbolBucket contains the data generated during placement, and is transferred to the main thread for rendering.
This eliminates the risky sharing of GeometryTile::buckets between the main thread and worker thread during TileWorker::redoPlacement.
While here, rationalize the names of states a SymbolLayout may be in:
* Pending: Waiting for the necessary glyphs or icons to be available.
* Prepared: The potential positions of text and icons have been determined.
* Placed: The final positions have been determined, taking into account prior layers.
In TileWorker, all SymbolLayouts are stored in a single vector. Each SymbolLayout knows what state it is in, and TileWorker can easily determine how much progress it can make toward a final result.
This paves the way for updates to filter and layout properties to trigger a source reload, without each SDK having to participate in the implementation.
