Mirror of metal.sx, talks to GLES3 via opengl.sx's runtime-loaded
fn-pointer variables. EGL bootstrap is owned by AndroidPlatform; this
module just calls `load_gl(@eglGetProcAddress)` once during `init` to
populate the pointers, then drives raw draw/state from there.
The renderer's vertex layout (12 floats: pos2/uv2/color4/params4 = 48
bytes, attribute locations 0-3) is hardcoded in a single shared VAO
the Gles3Gpu owns — `set_vertex_buffer` rebinds the active VBO against
it. `set_vertex_constants(slot=1, data, 64)` is treated as the 4x4
projection matrix; `set_texture(slot=0, ...)` binds texture unit 0 and
sets `uniform sampler2D uTex` — both match renderer.sx's shader
contract.
A subtle gotcha caught + recorded in the file header: declaring the
same GL name as a `#foreign` function while opengl.sx also declares it
as an fn-pointer global silently lets the global win, and calling
through the uninitialized variable jumps to PC=0. Solution: don't
re-declare; use opengl.sx's pointers and `load_gl` them.
renderer.sx: the GPU-protocol shader-source branch now passes
(UI_VERT_SRC_ES, UI_FRAG_SRC_ES) on Android (separate vert+frag) vs.
the combined MSL library on iOS. Both gated with `inline if OS == X`.
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