[client] egl: add cached uniforms and multipass effects

Replace the per-frame uniform list with stable, name-cached handles that
retain their values across shader recompilation. Track dirty uniforms so
only changed values are uploaded, reducing redundant GL calls and buffer
management.

Add a reusable effect-pass pipeline with per-pass shaders, samplers,
formats, resolutions, and intermediate render targets. This makes
external effects easier to integrate and supports arbitrary multipass
chains.

Migrate the desktop, cursor, damage, 24-bit, downscale, CAS, and FSR
rendering paths to the new APIs. Also ensure framebuffer objects are
released correctly.

client/renderers/EGL/effect.h

@@ -0,0 +1,53 @@
+/**
+ * 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
+ */
+
+#pragma once
+
+#include "egltypes.h"
+#include "shader.h"
+
+typedef struct EGL_Effect     EGL_Effect;
+typedef struct EGL_EffectPass EGL_EffectPass;
+typedef struct EGL_Texture    EGL_Texture;
+struct EGL_FilterRects;
+
+/*
+ * Effects execute their enabled passes in insertion order. Each pass owns an
+ * intermediate render target and sampler, while shaders remain caller-owned
+ * so they can be shared or selected at run time.
+ */
+bool egl_effectInit(EGL_Effect ** effect);
+void egl_effectFree(EGL_Effect ** effect);
+
+bool egl_effectAddPass(EGL_Effect * effect, EGL_Shader * shader,
+    EGL_EffectPass ** pass);
+
+void egl_effectPassSetShader(EGL_EffectPass * pass, EGL_Shader * shader);
+void egl_effectPassSetEnabled(EGL_EffectPass * pass, bool enabled);
+void egl_effectPassSetFilter(EGL_EffectPass * pass, GLenum minFilter,
+    GLenum magFilter);
+void egl_effectPassSetWrap(EGL_EffectPass * pass, GLenum wrapS,
+    GLenum wrapT);
+
+bool egl_effectPassSetup(EGL_EffectPass * pass, enum EGL_PixelFormat pixFmt,
+    unsigned int width, unsigned int height);
+
+EGL_Texture * egl_effectRun(EGL_Effect * effect,
+    struct EGL_FilterRects * rects, EGL_Texture * texture);