ThorVG pImpl idiom caused internal data to be scattered
across hierarchical classes. This refactoring consolidates
the data by inheriting pImpl internally, reducing memory
allocation counts and eliminating unnecessary strategy methods.
WebGL has a strict rule that does not allow the same GLBuffer
to be bound to both ARRAY_BUFFER and ELEMENT_ARRAY_BUFFER at the same time.
(https://registry.khronos.org/webgl/specs/latest/1.0/#5.14.5)
To support WebGL in the future, a separate GLBuffer is used to store index data.
* Use uniform block to pack all color informations
* Move the actual gl draw call into GlRenderer::sync function, so all
data is been uploaded into GPU
* Make GlRenderTask simple and generic for direct gl draw
