Rename vrKeyboard to steamKeyboardPatch; clipboard-sync on by default

- steamFrame.vrKeyboard -> steamFrame.steamKeyboardPatch (module, service
  and script names follow): it patches Steam's own on-screen keyboard
- clipboardSync.enable defaults to true: without it the nested desktop's
  clipboard is isolated

modules/session.nix

@@ -55,7 +55,7 @@ in {
       restart = lib.mkOption {
         type = lib.types.listOf lib.types.str;
         default = [ ];
-        example = [ "vr-keyboard.service" ];
+        example = [ "steam-keyboard-patch.service" ];
         description = "User units restarted on every switch (outer user manager).";
       };
       stop = lib.mkOption {