(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/plugin/grist-plugin-api.ts

@@ -133,7 +133,7 @@ export async function addImporter(name: string, path: string, mode: 'fullscreen'
  */
 export function ready(): void {
   rpc.processIncoming();
-  rpc.sendReadyMessage();
+  void rpc.sendReadyMessage();
 }
 
 function getPluginPath(location: Location) {