Move code to tui-winsource.h

Move code to tui-winsource.h

This moves code related to the execution info window from tui-data.h
to tui-winsource.h.  It fits better here because the execution info is
conceptually part of the source and disassembly windows, and
tui-winsource.h is where this common class lives.

gdb/ChangeLog
2019-08-13  Tom Tromey  <tom@tromey.com>

	* tui/tui-data.h (enum tui_bp_flag, tui_bp_flags, struct tui_source_element)
	(TUI_BP_HIT_POS, TUI_BP_BREAK_POS, TUI_EXEC_POS)
	(TUI_EXECINFO_SIZE, tui_exec_info_content): Move ...
	* tui/tui-winsource.h (enum tui_bp_flag, tui_bp_flags, struct
	tui_source_element, TUI_BP_HIT_POS, TUI_BP_BREAK_POS)
	(TUI_EXEC_POS, TUI_EXECINFO_SIZE, tui_exec_info_content):
	... here.