launcher: add a Cache shaders option, on by default

src/launcher/include/configuration.h

@@ -131,6 +131,7 @@ public:
 	bool                   sync_raw_image_buffers      = false;
 	bool                   tessellation_enabled        = false;
 	bool                   occlusion_queries_enabled   = false;
+	bool                   shader_cache_enabled        = true;
 	bool                   trophy_enabled              = true;
 	int                    trophy_duration_seconds     = 6;
 	bool                   perf_overlay_enabled        = false;
@@ -172,6 +173,7 @@ public:
 		sync_raw_image_buffers      = other.sync_raw_image_buffers;
 		tessellation_enabled        = other.tessellation_enabled;
 		occlusion_queries_enabled   = other.occlusion_queries_enabled;
+		shader_cache_enabled        = other.shader_cache_enabled;
 		trophy_enabled              = other.trophy_enabled;
 		trophy_duration_seconds     = other.trophy_duration_seconds;
 		perf_overlay_enabled        = other.perf_overlay_enabled;