API: allow custom getFileSystemEntries in DirectoryStructureHost.readDirectory

[ajafff]

I want to write a custom ParseConfigHost that uses a custom file system.
To implement ParseConfigHost.readDirectory I need to duplicate the whole logic of ts.matchFiles (in core.ts). Alternatively I can use ts.matchFiles directly although it is not exposed through the type declarations.

I propose to add an optional parameter getFileSystemEntries to ts.sys.readDirectory that is then passed to ts.matchFiles and falls back to getAccessibleFileSystemEntries if not provided.
That means the declaration of DirectoryStructureHost.readDirectory needs to be changed, too.
Alternatively you could just expose ts.matchFiles.