[client] egl: cache renderer GL state

Track context-local GL bindings to avoid redundant program, framebuffer,
buffer, texture, sampler, viewport, blend, and scissor state changes.

Invalidate the cache across context switches, ImGui rendering, and
shared object changes. Preserve CPU-backed texture upload correctness by
explicitly clearing pixel unpack buffer bindings where required.

This reduces hot-path driver overhead without adding waits or GPU
synchronization.

client/renderers/EGL/CMakeLists.txt

@@ -73,6 +73,7 @@ make_defines(
 add_library(renderer_EGL STATIC
   egl.c
   egldebug.c
+  state.c
   shader.c
   texture_util.c
   texture.c