Add lit components localization

Localization is performed via the @lit/localize package, which has been
integrated into the repo. A I18nLitElement class which extends
LitElement has been included, which automatically sets up the
localization.

This CL also introduces localization to the flattenThreads feature.

Fixed: twpowertools:157
Change-Id: If01540b9c8d70876a648aa002a1e0a5bede8f383
diff --git a/webpack.config.js b/webpack.config.js
index c515434..033685f 100644
--- a/webpack.config.js
+++ b/webpack.config.js
@@ -93,6 +93,10 @@
     },
     plugins: [
       new WebpackShellPluginNext({
+        onBuildStart: {
+          scripts: ['make lit_localize_build'],
+          blocking: true,
+        },
         onBuildEnd: {
           scripts:
               ['genmanifest -template templates/manifest.gjson -dest ' +
@@ -165,7 +169,8 @@
         new TerserPlugin({
           terserOptions: {
             format: {
-              ascii_only: true, // Due to https://iavm.xyz/b/twpowertools/145#c1
+              ascii_only:
+                  true,  // Due to https://iavm.xyz/b/twpowertools/145#c1
             },
           },
         }),