mesa: add new gl_driver_flags::NewWindowRectangles

This new driver flag will replace _NEW_SCISSOR which is
emitted when setting new window rectangles but it actually
triggers useless changes in the state tracker (like scissor
and rasterizer).

EXT_window_rectangles is currently only supported by Nouveau.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/mesa/main/mtypes.h

@@ -4397,6 +4397,11 @@ struct gl_driver_flags
     * gl_context::IntelConservativeRasterization
     */
    uint64_t NewIntelConservativeRasterization;
+
+   /**
+    * gl_context::Scissor::WindowRects
+    */
+   uint64_t NewWindowRectangles;
 };
 
 struct gl_uniform_buffer_binding