[WIP] FOR_ALL_TAB_WINDOWS cleanup. Add FOR_ALL_TABS and FOR_ALL_WINDOWS_IN_TAB.

Adds `FOR_ALL_TABS` and `FOR_ALL_WINDOWS_IN_TAB`. These combine together to make the `FOR_ALL_TAB_WINDOWS` helper that already existed.
`FOR_ALL_WINDOWS_IN_TAB` accounts for the above. `tp == curtab` check. I'm assuming this check should happen everywhere, so presumably we fix some bugs by using the helper in the places that previously didn't do this check.