Add Window::set_ime_purpose

This adds a way to set the purpose for the IME input, implemented
only on Wayland for now.

src/platform_impl/orbital/window.rs

@@ -12,6 +12,7 @@ use crate::{
     error,
     platform_impl::Fullscreen,
     window,
+    window::ImePurpose,
 };
 
 use super::{
@@ -323,6 +324,9 @@ impl Window {
     #[inline]
     pub fn set_ime_allowed(&self, _allowed: bool) {}
 
+    #[inline]
+    pub fn set_ime_purpose(&self, _purpose: ImePurpose) {}
+
     #[inline]
     pub fn focus_window(&self) {}