[lldb][NFC] Move Curses interface implementation to own file

Summary:
The IOHandler class source file is currently around 4600 LOC. However only 200
of these lines are concerned with the actual IOHandler class and the rest are the
implementations for Editline, IOHandlerConfirm and the Curses interface. All these
large features also cause that the IOHandler (which is in Core) has a large set of dependencies
on other parts of LLDB.

This patch splits out the code for the curses interface into its own file. This way
the simple IOHandler code is no longer buried in-between much larger functionalities.

Next up is splitting out the other IOHandlers into their own files and then move them
to more appropriate parts of LLDB.

Reviewers: labath, clayborg, JDevlieghere

Reviewed By: labath

Subscribers: mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D70946