osk-layouts: Fix Swiss layouts

Commit fe3a80ab9f added layouts for both Swiss French and Swiss
French, but as neither name matches the XKB layout code, they are
not used and the OSK falls back to the US layout.

The correct names are 'ch' (for Switch German) and 'ch+fr', so
rename the layout definitions accordingly.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5372

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2273>

data/gnome-shell-osk-layouts.gresource.xml

@@ -7,9 +7,10 @@
     <file>bg.json</file>
     <file>by.json</file>
     <file>ca.json</file>
+    <file>ch.json</file>
+    <file>ch+fr.json</file>
     <file>cz.json</file>
     <file>de.json</file>
-    <file>de+ch.json</file>
     <file>dk.json</file>
     <file>ee.json</file>
     <file>epo.json</file>
@@ -17,7 +18,6 @@
     <file>es.json</file>
     <file>fi.json</file>
     <file>fr.json</file>
-    <file>fr+ch.json</file>
     <file>ge.json</file>
     <file>gr.json</file>
     <file>hr.json</file>