(core) Speed up and upgrade build.

Summary:
- Upgrades to build-related packages:
  - Upgrade typescript, related libraries and typings.
  - Upgrade webpack, eslint; add tsc-watch, node-dev, eslint_d.

- Build organization changes:
  - Build webpack from original typescript, transpiling only; with errors still
    reported by a background tsc watching process.

- Typescript-related changes:
  - Reduce imports of AWS dependencies (very noticeable speedup)
  - Avoid auto-loading global @types
  - Client code is now built with isolatedModules flag (for safe transpilation)
  - Use allowJs to avoid copying JS files manually.

- Linting changes
  - Enhance Arcanist ESLintLinter to run before/after commands, and set up to use eslint_d
  - Update eslint config, and include .eslintignore to avoid linting generated files.
  - Include a bunch of eslint-prompted and eslint-generated fixes
  - Add no-unused-expression rule to eslint, and fix a few warnings about it

- Other items:
  - Refactor cssInput to avoid circular dependency
  - Remove a bit of unused code, libraries, dependencies

Test Plan: No behavior changes, all existing tests pass. There are 30 tests fewer reported because `test_gpath.py` was removed (it's been unused for years)

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D3498

app/client/lib/imports.js

@@ -8,7 +8,9 @@
 
 exports.loadBillingPage = () => import('app/client/ui/BillingPage' /* webpackChunkName: "BillingModule" */);
 exports.loadGristDoc = () => import('app/client/components/GristDoc' /* webpackChunkName: "GristDoc" */);
-exports.loadMomentTimezone = () => import('moment-timezone');
+// When importing this way, the module is under the "default" member, not sure why (maybe
+// esbuild-loader's doing).
+exports.loadMomentTimezone = () => import('moment-timezone').then(m => m.default);
 exports.loadPlotly = () => import('plotly.js-basic-dist' /* webpackChunkName: "plotly" */);
 exports.loadSearch = () => import('app/client/ui2018/search' /* webpackChunkName: "search" */);
 exports.loadUserManager = () => import('app/client/ui/UserManager' /* webpackChunkName: "usermanager" */);

app/client/lib/koSession.js

@@ -1,90 +0,0 @@
-/**
- * koSession offers observables whose values are tied to the browser session or history:
- *
- *    sessionValue(key)   - an observable preserved across history entries and reloads.
- *
- * Note: we could also support "browserValue", shared across all tabs and across browser restarts
- * (same as sessionValue but using window.localStorage), but it seems more appropriate to store
- * such values on the server.
- */
-
-/* global window, $ */
-
-var _ = require('underscore');
-var ko = require('knockout');
-
-/**
- * Maps a string key to an observable. The space of keys is shared for all kinds of observables,
- * and they differ only in where they store their state. Each observable gets several extra
- * properties:
- * @property {String} ksKey The key used for storage. It should be unique across koSession values.
- * @property {Object} ksDefault The default value if the storage doesn't have one.
- * @property {Function} ksFetch The method to fetch the value from storage.
- * @property {Function} ksSave The method to save the value to storage.
- */
-var _sessionValues = {};
-
-function createObservable(key, defaultValue, methods) {
-  var obs = _sessionValues[key];
-  if (!obs) {
-    _sessionValues[key] = obs = ko.observable();
-    obs.ksKey = key;
-    obs.ksDefaultValue = defaultValue;
-    obs.ksFetch = methods.fetch;
-    obs.ksSave = methods.save;
-    obs.dispose = methods.dispose;
-
-    // We initialize the observable before setting rateLimit, to ensure that the initialization
-    // doesn't end up triggering subscribers that are about to be added (which seems to be a bit
-    // of a problem with rateLimit extender, and possibly deferred). This workaround relies on the
-    // fact that the extender modifies its target without creating a new one.
-    obs(obs.ksFetch());
-    obs.extend({deferred: true});
-
-    obs.subscribe(function(newValue) {
-      if (newValue !== this.ksFetch()) {
-        console.log("koSession: %s changed %s -> %s", this.ksKey, this.ksFetch(), newValue);
-        this.ksSave(newValue);
-      }
-    }, obs);
-  }
-  return obs;
-}
-
-/**
- * Returns an observable whose value sticks across reloads and navigation, but is different for
- * different browser tabs. E.g. it may be used to reflect whether a side pane is open.
- * The `key` isn't visible to the user, so pick any unique string name.
- */
-function sessionValue(key, optDefault) {
-  return createObservable(key, optDefault, sessionValueMethods);
-}
-exports.sessionValue = sessionValue;
-
-var sessionValueMethods = {
-  'fetch': function() {
-    var value = window.sessionStorage.getItem(this.ksKey);
-    if (!value) {
-      return this.ksDefaultValue;
-    }
-    try {
-      return JSON.parse(value);
-    } catch (e) {
-      return this.ksDefaultValue;
-    }
-  },
-  'save': function(value) {
-    window.sessionStorage.setItem(this.ksKey, JSON.stringify(value));
-  },
-  'dispose': function(value) {
-    window.sessionStorage.removeItem(this.ksKey);
-  }
-};
-
-function onApplyState() {
-  _.each(_sessionValues, function(obs, key) {
-    obs(obs.ksFetch());
-  });
-}
-
-$(window).on('applyState', onApplyState);