Ref T13120. See PHI571. Fixes T5024. This adds a "View as Query" action to workboard columns, which builds a query in Maniphest that has the current query constraints plus an additional constraint to select only tasks in the specified column.
This is a normal query and can be turned into a dashboard panel, added to a menu, edited, saved as a link, etc.
Much of the complexity here is that finding tasks in a given column isn't entirely straightforward because of how board layout works: when you create a task, it isn't immediately placed in columns. It's only actually added to the "Backlog" column on any boards when someone looks at the board.
To get the right behavior, we must do "board layout" for any queried columns before we can constrain results. This isn't enormously efficient, but should be OK for reasonable boards.