FileHandle class not known in command-line MiniScript

[JoeStrout]

The result of a call like file.open is a FileHandle object, yet in command-line MiniScript, FileHandle is an unknown identifier. The class exists under the hood but we have no intrinsic reference to it. To reproduce, simply type:

FileHandle

at the REPL. You get an Undefined Identifier error.

(This works correctly in Mini Micro.)