Always create an execution info window for a source window

Always create an execution info window for a source window

A source or disassembly window will always have an "execution info"
window (the window along the side that displays breakpoint info), but
this isn't immediately clear from the source.  As a result, some code
has checks to see whether the execution_info is NULL.

This changes the source window base class to always instantiate an
execution_info window, then updates the rest of the code.  It also
simplifies window creation in tui-layout.c.

gdb/ChangeLog
2019-07-17  Tom Tromey  <tom@tromey.com>

	* tui/tui-winsource.c (tui_set_exec_info_content): Remove
	condition.
	* tui/tui-wingeneral.c (tui_source_window_base::make_visible):
	Remove condition.
	* tui/tui-source.c (tui_source_window_base::reset): New method.
	* tui/tui-layout.c (make_command_window): Don't call
	init_and_make_win.
	(make_source_window, make_disasm_window): Don't call
	make_source_or_disasm_window.
	(make_data_window): Don't call init_and_make_win.  Change calling
	convention.
	(show_source_disasm_command, show_data): Simplify.
	(make_source_or_disasm_window): Remove.
	(show_source_or_disasm_and_command): Simplify.
	* tui/tui-data.h (struct tui_gen_win_info) <reset>: Now virtual.
	(struct tui_source_window_base) <reset>: Likewise.
	<execution_info>: Remove initializer.
	* tui/tui-data.c (tui_source_window_base): Initialize
	execution_info.