Update frontend build system to shed old dependencies, and address fallout from that (#521)

* get tests working and update copyright headers

* lint fix

* eslint ts update

* update CI to use NPM

* fix CI

* prettier

* npm, not yarn for docker

* remove unused package

* bump dockerfile to latest node LTS and no need for cache clean

* make frontend Dockerfile work and remove unused SUBSTRATE_TELEMETRY_SAMPLE

* remove final yarn references

* add another comment

* remove unused import

* remove more unused deps

* comment typo

frontend/setupJest.js

@@ -0,0 +1,25 @@
+// Source code for the Substrate Telemetry Server.
+// Copyright (C) 2023 Parity Technologies (UK) Ltd.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+// This file runs some code before a jest test.
+
+// polyfill TextEncoder/TextDecoder since they aren't in jsdom:
+const { TextEncoder, TextDecoder } = require('util');
+global.TextEncoder = TextEncoder;
+global.TextDecoder = TextDecoder;
+
+// polyfill fetch since it's not in jsdom:
+require('whatwg-fetch');