(core) Speed up and upgrade build.

Summary:
- Upgrades to build-related packages:
  - Upgrade typescript, related libraries and typings.
  - Upgrade webpack, eslint; add tsc-watch, node-dev, eslint_d.

- Build organization changes:
  - Build webpack from original typescript, transpiling only; with errors still
    reported by a background tsc watching process.

- Typescript-related changes:
  - Reduce imports of AWS dependencies (very noticeable speedup)
  - Avoid auto-loading global @types
  - Client code is now built with isolatedModules flag (for safe transpilation)
  - Use allowJs to avoid copying JS files manually.

- Linting changes
  - Enhance Arcanist ESLintLinter to run before/after commands, and set up to use eslint_d
  - Update eslint config, and include .eslintignore to avoid linting generated files.
  - Include a bunch of eslint-prompted and eslint-generated fixes
  - Add no-unused-expression rule to eslint, and fix a few warnings about it

- Other items:
  - Refactor cssInput to avoid circular dependency
  - Remove a bit of unused code, libraries, dependencies

Test Plan: No behavior changes, all existing tests pass. There are 30 tests fewer reported because `test_gpath.py` was removed (it's been unused for years)

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D3498

buildtools/webpack.check.js

@@ -3,9 +3,26 @@ const path = require('path');
 module.exports = {
   target: 'web',
   mode: 'production',
-  entry: "./_build/app/client/browserCheck.js",
+  entry: "./app/client/browserCheck",
   output: {
     path: path.resolve("./static"),
     filename: "browser-check.js"
   },
+  resolve: {
+    extensions: ['.ts', '.js'],
+  },
+  module: {
+    rules: [
+      {
+        test: /\.(js|ts)?$/,
+        loader: 'esbuild-loader',
+        options: {
+          loader: 'ts',
+          target: 'es2017',
+          sourcemap: true,
+        },
+        exclude: /node_modules/
+      },
+    ]
+  }
 };