(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/Client.ts

@@ -12,12 +12,12 @@ import {Authorizer} from 'app/server/lib/Authorizer';
 import {ScopedSession} from 'app/server/lib/BrowserSession';
 import type {Comm} from 'app/server/lib/Comm';
 import {DocSession} from 'app/server/lib/DocSession';
-import * as log from 'app/server/lib/log';
+import log from 'app/server/lib/log';
 import {LogMethods} from "app/server/lib/LogMethods";
 import {shortDesc} from 'app/server/lib/shortDesc';
 import {fromCallback} from 'app/server/lib/serverUtils';
 import * as crypto from 'crypto';
-import * as moment from 'moment';
+import moment from 'moment';
 import * as WebSocket from 'ws';
 
 /// How many messages to accumulate for a disconnected client before booting it.