graphics: preserve logical alpha when blending reordered targets (PPSA02721)

Co-authored-by: EmK530 <admin@emk530.net>

src/graphics/shader/shader.h

@@ -178,6 +178,8 @@ struct ShaderPixelInputInfo {
 	bool                                           ps_sample_mask_export_enable = false;
 	bool                                           ps_sample_shading            = false;
 	bool                                           dual_source_blending         = false;
+	// Export logical alpha through MRT1 for blending after channel swizzling.
+	bool                                           alpha_blend_source_remap     = false;
 	bool                                           ps_early_z                   = false;
 	bool                                           ps_execute_on_noop           = false;
 	ShaderStageRuntime                             stage;