tablet: expose wlr_tablet_tool_v2_has_implicit_grab function

This is necessary so that sway can determine when to start emulating
pointer events -- it shouldn't start doing so during an implicit grab,
even if the pen is over a surface that doesn't bind tablet input.

Refs swaywm/sway#5302.

include/wlr/types/wlr_tablet_v2.h

@@ -253,6 +253,8 @@ void wlr_tablet_tool_v2_end_grab(struct wlr_tablet_v2_tablet_tool *tool);
 
 void wlr_tablet_tool_v2_start_implicit_grab(struct wlr_tablet_v2_tablet_tool *tool);
 
+bool wlr_tablet_tool_v2_has_implicit_grab(
+	struct wlr_tablet_v2_tablet_tool *tool);
 
 uint32_t wlr_send_tablet_v2_tablet_pad_enter(
 	struct wlr_tablet_v2_tablet_pad *pad,

types/tablet_v2/wlr_tablet_v2_tool.c

@@ -822,13 +822,14 @@ static const struct wlr_tablet_tool_v2_grab_interface
 	.cancel = implicit_tool_cancel,
 };
 
-static bool tool_has_implicit_grab(struct wlr_tablet_v2_tablet_tool *tool) {
+bool wlr_tablet_tool_v2_has_implicit_grab(
+		struct wlr_tablet_v2_tablet_tool *tool) {
 	return tool->grab->interface == &implicit_tool_grab_interface;
 }
 
 void wlr_tablet_tool_v2_start_implicit_grab(
 		struct wlr_tablet_v2_tablet_tool *tool) {
-	if (tool_has_implicit_grab(tool) || !tool->focused_surface) {
+	if (wlr_tablet_tool_v2_has_implicit_grab(tool) || !tool->focused_surface) {
 		return;
 	}