Move max_height method to tui_gen_win_info

Move max_height method to tui_gen_win_info

This moves the max_height method to tui_gen_win_info and implements it
in the subclasses.  This is used by a subsequent patch, which will
normalize window layout across all window types.

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

	* tui/tui-stack.h (struct tui_locator_window) <max_height>: New
	method.
	* tui/tui-regs.h (struct tui_data_item_window) <max_height>: New
	method.
	* tui/tui-data.h (struct tui_gen_win_info) <max_height>: New
	method.
	(struct tui_win_info) <max_height>: Now override.

Change-Id: I4ba3e8899bc4668328d3d78e3c1674c61882450d