(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/models/DataRowModel.ts

@@ -21,13 +21,12 @@ export class DataRowModel extends BaseRowModel {
   public _validationFailures: ko.PureComputed<Array<IRowModel<'_grist_Validations'>>>;
   public _isAddRow: ko.Observable<boolean>;
 
-  private _allValidationsList: ko.Computed<KoArray<ValidationRec>>;
   private _isRealChange: ko.Observable<boolean>;
 
   public constructor(dataTableModel: DataTableModel, colNames: string[]) {
     super(dataTableModel, colNames);
 
-    this._allValidationsList = dataTableModel.tableMetaRow.validations;
+    const allValidationsList: ko.Computed<KoArray<ValidationRec>> = dataTableModel.tableMetaRow.validations;
 
     this._isAddRow = ko.observable(false);
 
@@ -36,10 +35,10 @@ export class DataRowModel extends BaseRowModel {
     // changes, those should only be enabled when _isRealChange is true.
     this._isRealChange = ko.observable(true);
 
-    this._validationFailures = this.autoDispose(ko.pureComputed(function() {
-      return this._allValidationsList().all().filter(
+    this._validationFailures = this.autoDispose(ko.pureComputed(() => {
+      return allValidationsList().all().filter(
         validation => !this.cells[this.getValidationNameFromId(validation.id())]());
-    }, this));
+    }));
   }
 
   /**