fix: move utility types out of .d.ts file to fix exported declaration files (#6315)

src/utility-types.ts

@@ -0,0 +1,49 @@
+export type Mutable<T> = {
+  -readonly [P in keyof T]: T[P];
+};
+
+export type ValueOf<T> = T[keyof T];
+
+export type Merge<M, N> = Omit<M, keyof N> & N;
+
+/** utility type to assert that the second type is a subtype of the first type.
+ * Returns the subtype. */
+export type SubtypeOf<Supertype, Subtype extends Supertype> = Subtype;
+
+export type ResolutionType<T extends (...args: any) => any> = T extends (
+  ...args: any
+) => Promise<infer R>
+  ? R
+  : any;
+
+// https://github.com/krzkaczor/ts-essentials
+export type MarkOptional<T, K extends keyof T> = Omit<T, K> &
+  Partial<Pick<T, K>>;
+
+export type MarkRequired<T, RK extends keyof T> = Exclude<T, RK> &
+  Required<Pick<T, RK>>;
+
+export type MarkNonNullable<T, K extends keyof T> = {
+  [P in K]-?: P extends K ? NonNullable<T[P]> : T[P];
+} & { [P in keyof T]: T[P] };
+
+export type NonOptional<T> = Exclude<T, undefined>;
+
+// -----------------------------------------------------------------------------
+// type getter for interface's callable type
+// src: https://stackoverflow.com/a/58658851/927631
+// -----------------------------------------------------------------------------
+export type SignatureType<T> = T extends (...args: infer R) => any ? R : never;
+export type CallableType<T extends (...args: any[]) => any> = (
+  ...args: SignatureType<T>
+) => ReturnType<T>;
+// --------------------------------------------------------------------------—
+
+// Type for React.forwardRef --- supply only the first generic argument T
+export type ForwardRef<T, P = any> = Parameters<
+  CallableType<React.ForwardRefRenderFunction<T, P>>
+>[1];
+
+export type ExtractSetType<T extends Set<any>> = T extends Set<infer U>
+  ? U
+  : never;