(core) Faster builds all around.

Summary:
Building:
- Builds no longer wait for tsc for either client, server, or test targets. All use esbuild which is very fast.
- Build still runs tsc, but only to report errors. This may be turned off with `SKIP_TSC=1` env var.
- Grist-core continues to build using tsc.
- Esbuild requires ES6 module semantics. Typescript's esModuleInterop is turned
  on, so that tsc accepts and enforces correct usage.
- Client-side code is watched and bundled by webpack as before (using esbuild-loader)

Code changes:
- Imports must now follow ES6 semantics: `import * as X from ...` produces a
  module object; to import functions or class instances, use `import X from ...`.
- Everything is now built with isolatedModules flag. Some exports were updated for it.

Packages:
- Upgraded browserify dependency, and related packages (used for the distribution-building step).
- Building the distribution now uses esbuild's minification. babel-minify is no longer used.

Test Plan: Should have no behavior changes, existing tests should pass, and docker image should build too.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Subscribers: alexmojaki

Differential Revision: https://phab.getgrist.com/D3506

app/client/components/CustomView.ts

@@ -1,4 +1,4 @@
-import * as BaseView from 'app/client/components/BaseView';
+import BaseView from 'app/client/components/BaseView';
 import {Cursor} from 'app/client/components/Cursor';
 import * as commands from 'app/client/components/commands';
 import {GristDoc} from 'app/client/components/GristDoc';
@@ -7,9 +7,9 @@ import {ConfigNotifier, CustomSectionAPIImpl, GristDocAPIImpl, GristViewImpl,
         WidgetFrame} from 'app/client/components/WidgetFrame';
 import {CustomSectionElement, ViewProcess} from 'app/client/lib/CustomSectionElement';
 import {Disposable} from 'app/client/lib/dispose';
-import * as dom from 'app/client/lib/dom';
+import dom from 'app/client/lib/dom';
 import * as kd from 'app/client/lib/koDom';
-import * as DataTableModel from 'app/client/models/DataTableModel';
+import DataTableModel from 'app/client/models/DataTableModel';
 import {ViewSectionRec} from 'app/client/models/DocModel';
 import {CustomViewSectionDef} from 'app/client/models/entities/ViewSectionRec';
 import {UserError} from 'app/client/models/errors';