(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/uploads.ts

@@ -316,7 +316,7 @@ export async function createTmpDir(options: tmp.Options): Promise<TmpDirResult>
     try {
       // Still call the original callback, so that `tmp` module doesn't keep remembering about
       // this directory and doesn't try to delete it again on exit.
-      tmpCleanup();
+      await tmpCleanup();
     } catch (err) {
       // OK if it fails because the dir is already removed.
     }