GLES2: Add comments around EXT_shader_texture_lod check

To avoid reintroducing bugs as I did in #26928 and #26932.

texture2DLodEXT and textureCubeLodEXT are only for the fragment shader with
https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_shader_texture_lod.txt
In the vertex shader, texture2DLod and textureCubeLod are built-in.

drivers/gles2/shaders/canvas.glsl

@@ -220,29 +220,25 @@ VERTEX_SHADER_CODE
 /* clang-format off */
 [fragment]
 
+// texture2DLodEXT and textureCubeLodEXT are fragment shader specific.
+// Do not copy these defines in the [vertex] section.
 #ifndef USE_GLES_OVER_GL
-
 #ifdef GL_EXT_shader_texture_lod
 #extension GL_EXT_shader_texture_lod : enable
 #define texture2DLod(img, coord, lod) texture2DLodEXT(img, coord, lod)
 #define textureCubeLod(img, coord, lod) textureCubeLodEXT(img, coord, lod)
 #endif
-
-#endif
+#endif // !USE_GLES_OVER_GL
 
 #ifdef GL_ARB_shader_texture_lod
 #extension GL_ARB_shader_texture_lod : enable
 #endif
 
-
 #if !defined(GL_EXT_shader_texture_lod) && !defined(GL_ARB_shader_texture_lod)
 #define texture2DLod(img, coord, lod) texture2D(img, coord, lod)
 #define textureCubeLod(img, coord, lod) textureCube(img, coord, lod)
 #endif
 
-
-
-
 #ifdef USE_GLES_OVER_GL
 #define lowp
 #define mediump

drivers/gles2/shaders/cubemap_filter.glsl

@@ -25,15 +25,15 @@ void main() {
 /* clang-format off */
 [fragment]
 
+// texture2DLodEXT and textureCubeLodEXT are fragment shader specific.
+// Do not copy these defines in the [vertex] section.
 #ifndef USE_GLES_OVER_GL
-
 #ifdef GL_EXT_shader_texture_lod
 #extension GL_EXT_shader_texture_lod : enable
 #define texture2DLod(img, coord, lod) texture2DLodEXT(img, coord, lod)
 #define textureCubeLod(img, coord, lod) textureCubeLodEXT(img, coord, lod)
 #endif
-
-#endif
+#endif // !USE_GLES_OVER_GL
 
 #ifdef GL_ARB_shader_texture_lod
 #extension GL_ARB_shader_texture_lod : enable
@@ -44,8 +44,6 @@ void main() {
 #define textureCubeLod(img, coord, lod) textureCube(img, coord, lod)
 #endif
 
-
-
 #ifdef USE_GLES_OVER_GL
 #define lowp
 #define mediump

drivers/gles2/shaders/scene.glsl

@@ -675,15 +675,15 @@ VERTEX_SHADER_CODE
 /* clang-format off */
 [fragment]
 
+// texture2DLodEXT and textureCubeLodEXT are fragment shader specific.
+// Do not copy these defines in the [vertex] section.
 #ifndef USE_GLES_OVER_GL
-
 #ifdef GL_EXT_shader_texture_lod
 #extension GL_EXT_shader_texture_lod : enable
 #define texture2DLod(img, coord, lod) texture2DLodEXT(img, coord, lod)
 #define textureCubeLod(img, coord, lod) textureCubeLodEXT(img, coord, lod)
 #endif
-
-#endif
+#endif // !USE_GLES_OVER_GL
 
 #ifdef GL_ARB_shader_texture_lod
 #extension GL_ARB_shader_texture_lod : enable
@@ -694,9 +694,6 @@ VERTEX_SHADER_CODE
 #define textureCubeLod(img, coord, lod) textureCube(img, coord, lod)
 #endif
 
-
-
-
 #ifdef USE_GLES_OVER_GL
 #define lowp
 #define mediump