Refine Window::set_cursor_grab API

This commit renames `Window::set_cursor_grab` to
`Window::set_cursor_grab_mode`. The new API now accepts enumeration
to control the way cursor grab is performed. The value could be: `lock`,
`confine`, or `none`.

This commit also implements `Window::set_cursor_position` for Wayland,
since it's tied to locked cursor.

Implements API from #1677.

src/platform_impl/web/web_sys/canvas.rs

@@ -89,8 +89,8 @@ impl Canvas {
         })
     }
 
-    pub fn set_cursor_grab(&self, grab: bool) -> Result<(), RootOE> {
-        if grab {
+    pub fn set_cursor_lock(&self, lock: bool) -> Result<(), RootOE> {
+        if lock {
             self.raw().request_pointer_lock();
         } else {
             let window = web_sys::window()