text: Add support for control keys to the protocol

Add key event to the text_model interface and a key request to the
input_method_context interface. Implement it in the example editor
client and the example keyboard.

Signed-off-by: Jan Arne Petersen <jpetersen@openismus.com>

protocol/input-method.xml

@@ -53,6 +53,10 @@
       <arg name="index" type="int"/>
       <arg name="length" type="uint"/>
     </request>
+    <request name="key">
+      <arg name="key" type="uint"/>
+      <arg name="state" type="uint"/>
+    </request>
     <event name="surrounding_text">
       <description summary="surrounding text event">
         The plain surrounding text around the input position. Cursor is the

protocol/text.xml

@@ -89,7 +89,10 @@
       <arg name="length" type="uint"/>
     </event>
     <event name="preedit_styling"/>
-    <event name="key"/>
+    <event name="key">
+      <arg name="key" type="uint"/>
+      <arg name="state" type="uint"/>
+    </event>
     <event name="selection_replacement"/>
     <event name="direction"/>
     <event name="locale"/>