new splits don't invoke `onSetActive`

Description of the problem or steps to reproduce

The callback function onSetActive is not called when creating a split, for example via hsplit or vsplit. In contrast, it is called when creating a new tab. I think it should also be called for new splits because the bufpane changes. When navigating between bufpanes with NextSplit, onSetActive is called.

For completeness, here is the function I used to check this:

function onSetActive(bp)
    micro.TermMessage("onSetActive <", bp.Buf.Path, "> <", bp.Buf.AbsPath, "> <", bp:Name(), ">")
    return true
end

ADDED: Also, when closing a tab (i.e., closing a bufpane in a tab without split), onSetActive is not called for the bufpane that is activated in the next tab.

Specifications

Commit hash: fb208180
OS: Ubuntu
Terminal: urxvt

Start by tracing the code paths for creating splits via hsplit and vsplit, then compare them with new-tab creation and NextSplit, where onSetActive is already called. Also trace closing a tab and activating the next tab's bufpane. Done means onSetActive is invoked for newly active bufpanes in both split creation and tab closing cases.