(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/tsconfig-base.json

@@ -1,10 +1,12 @@
 {
   "compilerOptions": {
     "allowSyntheticDefaultImports": true,
-    "target": "es2016",
+    "target": "es2017",
     "module": "commonjs",
     "strict": true,
     "strictPropertyInitialization": false,
+    "useUnknownInCatchVariables": false,
+    "skipLibCheck": true,
     "sourceMap": true,
     "noImplicitAny": true,
     "noUnusedLocals": true,
@@ -22,6 +24,7 @@
       ],
     },
     "composite": true,
+    "types" : [],
     "plugins": [{
       "name": "typescript-eslint-language-service"
     }],