(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

test/server/lib/Authorizer.ts

@@ -10,7 +10,7 @@ import {configForUser, getGristConfig} from 'test/gen-server/testUtils';
 import {createDocTools} from 'test/server/docTools';
 import {openClient} from 'test/server/gristClient';
 import * as testUtils from 'test/server/testUtils';
-import * as uuidv4 from 'uuid/v4';
+import uuidv4 from 'uuid/v4';
 
 let serverUrl: string;
 let server: FlexServer;

test/server/lib/DocApi.ts

@@ -11,7 +11,7 @@ import {
   docPeriodicApiUsageKey,
   getDocApiUsageKeysToIncr
 } from 'app/server/lib/DocApi';
-import * as log from 'app/server/lib/log';
+import log from 'app/server/lib/log';
 import {exitPromise} from 'app/server/lib/serverUtils';
 import {connectTestingHooks, TestingHooksClient} from 'app/server/lib/TestingHooks';
 import axios, {AxiosResponse} from 'axios';
@@ -19,10 +19,10 @@ import {delay} from 'bluebird';
 import * as bodyParser from 'body-parser';
 import {assert} from 'chai';
 import {ChildProcess, execFileSync, spawn} from 'child_process';
-import * as FormData from 'form-data';
+import FormData from 'form-data';
 import * as fse from 'fs-extra';
 import * as _ from 'lodash';
-import * as LRUCache from 'lru-cache';
+import LRUCache from 'lru-cache';
 import * as moment from 'moment';
 import fetch from 'node-fetch';
 import {tmpdir} from 'os';