opengl: added SDL_HINT_OPENGL_FORCE_SRGB_CAPABLE.

Reference Issue #14898.

(cherry picked from commit 632c83b722)

include/SDL3/SDL_hints.h

@@ -3006,6 +3006,42 @@ extern "C" {
  */
 #define SDL_HINT_OPENGL_ES_DRIVER "SDL_OPENGL_ES_DRIVER"
 
+/**
+ * A variable controlling whether to force an sRGB-capable OpenGL context.
+ *
+ * At OpenGL context creation time, some platforms can request an sRGB-capable
+ * context. However, sometimes any form of the request can cause surprising
+ * results on some drivers, platforms, and hardware. Usually the surprise is
+ * in the form of rendering that is either a little darker or a little
+ * brighter than intended.
+ *
+ * This hint allows the user to override the app's sRGB requests and either
+ * force a specific value, or avoid requesting anything at all, depending on
+ * what makes things work correctly for their system.
+ *
+ * This is meant as a fail-safe; apps should probably not explicitly set this,
+ * and most users should not, either.
+ *
+ * Note that some platforms cannot make this request at all, and on all
+ * platforms this request can be denied by the operating system.
+ *
+ * The variable can be set to the following values:
+ *
+ * - "0": Force a request for an OpenGL context that is _not_ sRGB-capable.
+ * - "1": Force a request for an OpenGL context that _is_ sRGB-capable.
+ * - "skip": Don't make any request for an sRGB-capable context
+ *   (don't specify the attribute at all during context creation time).
+ * - any other string is undefined behavior.
+ *
+ * If unset, or set to an empty string, SDL will make a request using the
+ * value the app specified with the SDL_GL_FRAMEBUFFER_SRGB_CAPABLE attribute.
+ *
+ * This hint should be set before an OpenGL context is created.
+ *
+ * \since This hint is available since SDL 3.4.2.
+ */
+#define SDL_HINT_OPENGL_FORCE_SRGB_CAPABLE "SDL_OPENGL_FORCE_SRGB_CAPABLE"
+
 /**
  * Mechanism to specify openvr_api library location
  *