Separate out data window

Separate out data window

This removes "data_window" from union tui_which_element and updates
the uses.  It also changes how tui_data_window refers to the register
data, and changes it not to need the "content" field at all (though as
this is in a base class, it can't yet be removed).

gdb/ChangeLog
2019-06-25  Tom Tromey  <tom@tromey.com>

	* tui/tui-wingeneral.c (tui_data_window::refresh_window): Update.
	* tui/tui-windata.c (tui_data_window::first_data_item_displayed)
	(tui_delete_data_content_windows, tui_display_all_data)
	(tui_data_window::do_scroll_vertical, tui_display_data_from):
	Update.
	* tui/tui-win.c (tui_data_window::set_new_height): Simplify.
	* tui/tui-regs.c (tui_last_regs_line_no)
	(tui_line_from_reg_element_no, tui_first_reg_element_no_inline)
	(tui_show_registers): Update.
	(tui_show_register_group): Return void.  Update.
	(tui_display_registers_from, tui_display_reg_element_at_line)
	(tui_display_registers_from_line, tui_check_register_values):
	Update.
	* tui/tui-data.h (union tui_which_element) <data_window>: Remove
	member.
	(struct tui_data_window) <regs_content>: Now a std::vector.
	<regs_content_count>: Remove.
	(tui_add_content_elements, tui_free_data_content): Don't declare.
	* tui/tui-data.c (tui_data_window::clear_detail): Update.
	(init_content_element): Remove DATA_WIN case.  Add assert.
	(tui_add_content_elements): Remove.
	(tui_data_window): Update.
	(tui_free_data_content): Remove.
	(free_content_elements): Remove DATA_WIN case.