Speed up and simplify translations build (#19988)

* Speed up and simplify translations build

- Remove use of gulp-flatmap for merges (wasted input) and just loop over translation files.
- Parse and buffer master only once for all merges.
- Remove lokalise key reference transform from non-English files. This is already done by Lokalise when they are downloaded.
- Remove tabs from merged output to minimize buffer sizes.
- Pipe merges to a hashing stream, removing extra tasks and intermediate file I/O.
- Pipe hashed files to a single custom asynchronous transform stream to fragmentize the files. It expands the stream to push a new file for each fragment.
- Incorporate flattening into fragmentization.
- Delete entire ui.panel key for base translation (instead of leaving an empty object).
- Optimize flatten method to stop copying output over and over.
- Convert empty and test filters to JSON.parse() revivers for simplicity and better performance.
- Incorporate supervisor builds into main tasks using a simple toggle (i.e. remove duplicate code).
- Funcify local tasks and simplify exported tasks.
- Incorporate test metadata task into a simplified metadata task.

* Fix Lokalise key reference link

Co-authored-by: Simon Lamon <32477463+silamon@users.noreply.github.com>

---------

Co-authored-by: Simon Lamon <32477463+silamon@users.noreply.github.com>

build-scripts/gulp/webpack.js

@@ -99,7 +99,7 @@ gulp.task("webpack-watch-app", () => {
   ).watch({ poll: isWsl }, doneHandler());
   gulp.watch(
     path.join(paths.translations_src, "en.json"),
-    gulp.series("create-translations", "copy-translations-app")
+    gulp.series("build-translations", "copy-translations-app")
   );
 });