Convert most of core.ts to accept ReadonlyArray (#17092)

* Convert most of core.ts to accept ReadonlyArray

* Fix lint

* Fix isArray

src/harness/virtualFileSystem.ts

@@ -216,7 +216,7 @@ namespace Utils {
             }
         }
 
-        readDirectory(path: string, extensions: string[], excludes: string[], includes: string[], depth: number) {
+        readDirectory(path: string, extensions: ReadonlyArray<string>, excludes: ReadonlyArray<string>, includes: ReadonlyArray<string>, depth: number) {
             return ts.matchFiles(path, extensions, excludes, includes, this.useCaseSensitiveFileNames, this.currentDirectory, depth, (path: string) => this.getAccessibleFileSystemEntries(path));
         }
     }