Consistently 'use strict' for JS code

Change-Id: I6f6e06ad32ffa87242f5a0f41c176149b754e2ea
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/169187
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <stephan.bergmann@allotropia.de>

static/emscripten/environment.js

@@ -1,3 +1,5 @@
+'use strict';
+
 if (!('preRun' in Module)) Module['preRun'] = [];
 Module.preRun.push(function() {
     ENV.SAL_LOG = "+WARN"

static/emscripten/soffice_args.js

@@ -1,3 +1,5 @@
+'use strict';
+
 Module['arguments'] = [
     '--norestore',
     '--nologo',

static/emscripten/uno.js

@@ -7,6 +7,8 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
+'use strict';
+
 Module.initUno = function() {
     if (Module.uno === undefined) {
         Module.uno = init_unoembind_uno(Module);

unotest/source/embindtest/embindtest.js

@@ -7,6 +7,8 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
+'use strict';
+
 Module.addOnPostRun(function() {
     console.log('Running embindtest');
     Module.initUno();