Allow TUI windows in Python

Allow TUI windows in Python

This patch adds support for writing new TUI windows in Python.

2020-02-22  Tom Tromey  <tom@tromey.com>

	* NEWS: Add entry for gdb.register_window_type.
	* tui/tui-layout.h (window_factory): New typedef.
	(tui_register_window): Declare.
	* tui/tui-layout.c (saved_tui_windows): New global.
	(tui_apply_current_layout): Use it.
	(tui_register_window): New function.
	* python/python.c (do_start_initialization): Call
	gdbpy_initialize_tui.
	(python_GdbMethods): Add "register_window_type" function.
	* python/python-internal.h (gdbpy_register_tui_window)
	(gdbpy_initialize_tui): Declare.
	* python/py-tui.c: New file.
	* Makefile.in (SUBDIR_PYTHON_SRCS): Add py-tui.c.

gdb/doc/ChangeLog
2020-02-22  Tom Tromey  <tom@tromey.com>

	* python.texi (Python API): Add menu item.
	(TUI Windows In Python): New node.

gdb/testsuite/ChangeLog
2020-02-22  Tom Tromey  <tom@tromey.com>

	* gdb.python/tui-window.exp: New file.
	* gdb.python/tui-window.py: New file.

Change-Id: I85fbfb923a1840450a00a7dce113a05d7f048baa