(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/server/lib/ITestingHooks.ts

@@ -1,8 +1,8 @@
 import {UserProfile} from 'app/common/LoginSessionAPI';
 
 export interface ITestingHooks {
-  getOwnPort(): number;
-  getPort(): number;
+  getOwnPort(): Promise<number>;
+  getPort(): Promise<number>;
   updateAuthToken(instId: string, authToken: string): Promise<void>;
   getAuthToken(instId: string): Promise<string|null>;
   useTestToken(instId: string, token: string): Promise<void>;