(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/ui/VisibleFieldsConfig.ts

@@ -352,7 +352,7 @@ function getFieldNewPosition(fields: KoArray<ViewFieldRec>, item: IField,
   return tableUtil.fieldInsertPositions(fields, index, 1)[0];
 }
 
-function getItemIndex<T>(collection: KoArray<ViewFieldRec>, item: ViewFieldRec|null): number {
+function getItemIndex(collection: KoArray<ViewFieldRec>, item: ViewFieldRec|null): number {
   if (item !== null) {
     return collection.peek().indexOf(item);
   }