qmp: qmp_send_key(): accept key codes in hex

Before the qapi conversion, the sendkey command could be used to
send key codes in hex directly to the guest. In HMP, this would
be like:

 (qemu) sendkey 0xdc

However, the qapi conversion broke this, as it only supports sending
QKeyCode values to the guest. That's a regression.

This commit fixes the problem by adding hex value support down
the QMP interface, qmp_send_key().

In more detail, this commit:

 1. Adds the KeyValue union. This can represent an hex value or
    a QKeyCode value

 2. *Changes* the QMP send-key command to take an KeyValue argument
    instead of a QKeyCode one

 3. Adapt hmp_send_key() to the QMP interface changes

Item 2 is an incompatible change, but as we're in development phase
(and this command has been merged a few weeks ago) this shouldn't be
a problem.

Finally, it's not possible to split this commit without breaking the
build.

Reported-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
diff --git a/qapi-schema.json b/qapi-schema.json
index c6a6767..28d8815 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -2621,12 +2621,26 @@
              'lf', 'help', 'meta_l', 'meta_r', 'compose' ] }
 
 ##
+# @KeyValue
+#
+# Represents a keyboard key.
+#
+# Since: 1.3.0
+##
+{ 'union': 'KeyValue',
+  'data': {
+    'number': 'int',
+    'qcode': 'QKeyCode' } }
+
+##
 # @send-key:
 #
 # Send keys to guest.
 #
-# @keys: key sequence. 'keys' is the name of the key. Use a JSON array to
-#        press several keys simultaneously.
+# @keys: An array of @KeyValue elements. All @KeyValues in this array are
+#        simultaneously sent to the guest. A @KeyValue.number value is sent
+#        directly to the guest, while @KeyValue.qcode must be a valid
+#        @QKeyCode value
 #
 # @hold-time: #optional time to delay key up events, milliseconds. Defaults
 #             to 100
@@ -2638,7 +2652,7 @@
 #
 ##
 { 'command': 'send-key',
-  'data': { 'keys': ['QKeyCode'], '*hold-time': 'int' } }
+  'data': { 'keys': ['KeyValue'], '*hold-time': 'int' } }
 
 ##
 # @screendump: