(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

app/client/widgets/NewAbstractWidget.ts

@@ -14,6 +14,7 @@ import {
   dom,
   DomContents,
   fromKo,
+  IDisposableOwnerT,
   Observable,
 } from 'grainjs';
 
@@ -30,8 +31,13 @@ export abstract class NewAbstractWidget extends Disposable {
   /**
    * Override the create() method to match the parameters of create() expected by FieldBuilder.
    */
-  public static create(field: ViewFieldRec) {
-    return Disposable.create.call(this as any, null, field);
+  // We copy Disposable.create() signature (the second one) to pacify typescript, but code must
+  // use the first signature, which is compatible with old-style constructors.
+  public static create<T extends new (...args: any[]) => any>(field: ViewFieldRec): InstanceType<T>;
+  public static create<T extends new (...args: any[]) => any>(
+    this: T, owner: IDisposableOwnerT<InstanceType<T>>|null, ...args: ConstructorParameters<T>): InstanceType<T>;
+  public static create(...args: any[]) {
+    return Disposable.create.call(this as any, null, ...args);
   }
 
   protected options: SaveableObjObservable<any>;