(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/DocApi.ts

@@ -58,16 +58,16 @@ import {localeFromRequest} from "app/server/lib/ServerLocale";
 import {allowedEventTypes, isUrlAllowed, WebhookAction, WebHookSecret} from "app/server/lib/Triggers";
 import {handleOptionalUpload, handleUpload} from "app/server/lib/uploads";
 import * as assert from 'assert';
-import * as contentDisposition from 'content-disposition';
+import contentDisposition from 'content-disposition';
 import {Application, NextFunction, Request, RequestHandler, Response} from "express";
 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 * as path from 'path';
 import * as t from "ts-interface-checker";
 import {Checker} from "ts-interface-checker";
-import * as uuidv4 from "uuid/v4";
+import uuidv4 from "uuid/v4";
 
 // Cap on the number of requests that can be outstanding on a single document via the
 // rest doc api.  When this limit is exceeded, incoming requests receive an immediate