Implement text cursor position protocol.

Here we create a new client/compositor interface in weston to allow
clients to report their x/y cursor position to the compositor. These
values are then used to center the zoom area on this point. This
is useful for everyone, especially people who are visually impaired.
diff --git a/clients/window.h b/clients/window.h
index 7e968d0..a8537b3 100644
--- a/clients/window.h
+++ b/clients/window.h
@@ -307,6 +307,9 @@
 const char *
 window_get_title(struct window *window);
 
+void
+window_set_text_cursor_position(struct window *window, int32_t x, int32_t y);
+
 int
 widget_set_tooltip(struct widget *parent, char *entry, float x, float y);