Bug 1487581 - Create aboutdebugging.ftl and use it as localization file in aboutdebugging-new;r=daisuke,flod

Depends on D23871

Differential Revision: https://phabricator.services.mozilla.com/D23872

--HG--
extra : moz-landing-system : lando

devtools/client/aboutdebugging-new/src/modules/l10n.js

@@ -25,8 +25,10 @@ class L10n {
     }
 
     const locales = Services.locale.appLocalesAsBCP47;
-    const generator =
-      L10nRegistry.generateBundles(locales, ["aboutdebugging.ftl"]);
+    const generator = L10nRegistry.generateBundles(locales, [
+      "aboutdebugging.ftl",
+      "devtools/aboutdebugging.ftl",
+    ]);
 
     this._bundles = [];
     for await (const bundle of generator) {

devtools/client/locales/en-US/aboutdebugging.ftl

@@ -0,0 +1,5 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+### These strings are used inside the about:debugging UI.