(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/server/lib/FlexServer.ts

@@ -39,7 +39,7 @@ import {HostedStorageManager} from 'app/server/lib/HostedStorageManager';
 import {IBilling} from 'app/server/lib/IBilling';
 import {IDocStorageManager} from 'app/server/lib/IDocStorageManager';
 import {INotifier} from 'app/server/lib/INotifier';
-import * as log from 'app/server/lib/log';
+import log from 'app/server/lib/log';
 import {getLoginSystem} from 'app/server/lib/logins';
 import {IPermitStore} from 'app/server/lib/Permit';
 import {getAppPathTo, getAppRoot, getUnpackedAppRoot} from 'app/server/lib/places';
@@ -59,12 +59,12 @@ import {addUploadRoute} from 'app/server/lib/uploads';
 import {buildWidgetRepository, IWidgetRepository} from 'app/server/lib/WidgetRepository';
 import axios from 'axios';
 import * as bodyParser from 'body-parser';
-import * as express from 'express';
+import express from 'express';
 import * as fse from 'fs-extra';
 import * as http from 'http';
 import * as https from 'https';
 import mapValues = require('lodash/mapValues');
-import * as morganLogger from 'morgan';
+import morganLogger from 'morgan';
 import {AddressInfo} from 'net';
 import fetch from 'node-fetch';
 import * as path from 'path';