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>

gulpfile.js

@@ -1,4 +1,7 @@
 import { globIterate } from "glob";
+import { availableParallelism } from "node:os";
+
+process.env.UV_THREADPOOL_SIZE = availableParallelism();
 
 const gulpImports = [];