Fix Omit type to work on types that don't have an index signature

Author: Ben Grynhaus

libs/core/src/lib/declarations/omit.d.ts

@@ -3,5 +3,9 @@
 
 import { IndexSignature } from './index-signature';
 import { KnownKeys } from './known-keys';
+import { UnknownKeys } from './unknown-keys';
 
-export type Omit<T, K extends keyof T> = Pick<T, Exclude<KnownKeys<T> & keyof T, K>> & IndexSignature<T>;
+export type _KnownKeysOmit<T, K extends keyof T> = Pick<T, Exclude<KnownKeys<T> & keyof T, K>>;
+export type Omit<T, K extends keyof T> = UnknownKeys<T> extends never
+  ? _KnownKeysOmit<T, K>
+  : _KnownKeysOmit<T, K> & IndexSignature<T>;

libs/core/src/lib/declarations/unknown-keys.d.ts

@@ -0,0 +1,5 @@
+export type UnknownKeys<T> = { [K in keyof T]: string extends K ? K : number extends K ? K : never } extends {
+  [_ in keyof T]: infer U
+}
+  ? U
+  : never;