[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/state.c

@@ -0,0 +1,55 @@
+/**
+ * Looking Glass
+ * Copyright © 2017-2026 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include "state.h"
+
+#include <stdatomic.h>
+#include <string.h>
+
+_Thread_local EGL_StateCache g_eglState;
+static _Thread_local unsigned int localGeneration;
+static atomic_uint sharedGeneration = 1;
+
+static void stateInvalidate(unsigned int generation)
+{
+  memset(&g_eglState, 0, sizeof(g_eglState));
+  localGeneration = generation;
+}
+
+void egl_stateInvalidate(void)
+{
+  stateInvalidate(atomic_load_explicit(
+      &sharedGeneration, memory_order_relaxed));
+}
+
+void egl_stateInvalidateShared(void)
+{
+  const unsigned int generation = atomic_fetch_add_explicit(
+      &sharedGeneration, 1, memory_order_release) + 1;
+  stateInvalidate(generation);
+}
+
+void egl_stateCheckShared(void)
+{
+  const unsigned int generation = atomic_load_explicit(
+      &sharedGeneration, memory_order_acquire);
+  if (localGeneration != generation)
+    stateInvalidate(generation);
+}