(core) Configure more comprehensive eslint rules for Typescript

Summary:
- Update rules to be more like we've had with tslint
- Switch tsserver plugin to eslint (tsserver makes for a much faster way to lint in editors)
- Apply suggested auto-fixes
- Fix all lint errors and warnings in core/, app/, test/

Test Plan: Some behavior may change subtly (e.g. added missing awaits), relying on existing tests to catch problems.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2785

app/client/lib/autocomplete.ts

@@ -1,7 +1,7 @@
 /**
  * Implements an autocomplete dropdown.
  */
-import {createPopper, Instance as Popper, Modifier, Options as PopperOptions} from '@popperjs/core';
+import {createPopper, Modifier, Instance as Popper, Options as PopperOptions} from '@popperjs/core';
 import {ACItem, ACResults, HighlightFunc} from 'app/client/lib/ACIndex';
 import {reportError} from 'app/client/models/errors';
 import {Disposable, dom, EventCB, IDisposable} from 'grainjs';