Add workaround for using bundler as the module-resolution in TypeScript (#744)

Co-authored-by: Sindre Sorhus <[email protected]>

Author: Borewit

core.d.ts

@@ -194,6 +194,11 @@ export type AnyWebReadableByteStreamWithFileType = AnyWebReadableStream<Uint8Arr
 	readonly fileType?: FileTypeResult;
 };
 
+/**
+Workaround for using `bundler` as the module-resolution in TypeScript.
+*/
+export function fileTypeFromFile(filePath: string, options?: {customDetectors?: Iterable<Detector>}): Promise<FileTypeResult | undefined>;
+
 /**
 Returns a `Promise` which resolves to the original readable stream argument, but with an added `fileType` property, which is an object like the one returned from `fileTypeFromFile()`.