gdbus-codegen: Don't generate invalid GObject property names

For a D-Bus property with name "Type" (fairly common), we used to
generate a GObject property with name "type-" and C accessors
get_type_() (to avoid clashing with the GType getter), set_type_()
(for symmetri).

However, the rules for GObject property names are fairly rigid and
specifically prohibit names ending in a dash.

Therefore change things so the chosen GObject property name is "type"
but preserve the naming rules for the C getter and setter (for the
same reasons: avoiding name clashing and symmetri).

This change does break the API of generated code (but only on the
GObject property level, the C symbols are not changed) but strictly
speaking the behavior was undefined since "type-" was an invalid
GObject property name.

Also add a test case for this.

Bug 679473.

https://bugzilla.gnome.org/show_bug.cgi?id=679473

Signed-off-by: David Zeuthen <zeuthen@gmail.com>

gio/tests/test-codegen.xml

@@ -475,4 +475,8 @@
     </method>
   </interface>
 
+  <interface name="Naming">
+    <property name="Type" type="i" access="readwrite"/>
+  </interface>
+
 </node>