First use of tui_layout

First use of tui_layout

This patch introduces the first use of tui_layout, by changing
show_layout to clone and use the appropriate tui_layout.

This resulted in one minor layout change, and also in the unintended
-- but good -- side effect that the title of each boxed window is now
visible.

gdb/ChangeLog
2019-12-11  Tom Tromey  <tom@tromey.com>

	* tui/tui-layout.h (tui_apply_current_layout): Declare.
	* tui/tui-layout.c (standard_layouts, applied_layout): New
	globals.
	(tui_apply_current_layout): New function.
	(show_layout): Set applied_layout.  Call
	tui_apply_current_layout.
	(show_source_command, show_disasm_command)
	(show_source_disasm_command, show_data)
	(show_source_or_disasm_and_command): Remove.
	(initialize_layouts): New function.
	(_initialize_tui_layout): Call initialize_layouts.

gdb/testsuite/ChangeLog
2019-12-11  Tom Tromey  <tom@tromey.com>

	* gdb.tui/regs.exp: Update.
	* gdb.tui/empty.exp (layouts): Update.
	* gdb.tui/basic.exp: Update.
	* lib/tuiterm.exp (_check_box): Don't check bottom border.

Change-Id: If1ee06ee58f4803e8c213f4ab0f5bb59f4650ec2