(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/BillingForm.ts

@@ -153,7 +153,7 @@ class BillingPaymentForm extends BillingSubForm {
   }) {
     super();
     const autofill = this._options.autofill;
-    const stripeAPIKey = (G.window as any).gristConfig.stripeAPIKey;
+    const stripeAPIKey = G.window.gristConfig.stripeAPIKey;
     try {
       this._stripe = G.Stripe(stripeAPIKey);
       this._elements = this._stripe.elements();
@@ -462,7 +462,7 @@ function checkRequired(propertyName: string) {
 // if the current observable value is valid.
 function createValidated(
   owner: IDisposableOwnerT<any>,
-  checkValidity: (value: string) => void
+  checkValidity: (value: string) => void|Promise<void>,
 ): IValidated<string> {
   const value = Observable.create(owner, '');
   const isInvalid = Observable.create<boolean>(owner, false);

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);
   }