sokol: add mouse cursor support (#15111)

examples/gg/cursor.v

@@ -0,0 +1,24 @@
+module main
+
+import gg
+import gx
+import sokol.sapp
+
+fn main() {
+	gg.new_context(
+		bg_color: gx.white
+		window_title: 'Cursor'
+		frame_fn: frame
+		init_fn: init
+	).run()
+}
+
+fn init(mut ctx gg.Context) {
+	sapp.set_mouse_cursor(.ibeam)
+}
+
+fn frame(mut ctx gg.Context) {
+	ctx.begin()
+	ctx.draw_text_def(10, 25, 'Your cursor should be an I shaped beam.')
+	ctx.end()
+}