This is a small refactor on my way to much bigger, more painful refactors. This PR does five things:
* `TermControl.*` has historically had all the control-relevant EventArgs defined in the same file as TermControl. That's just added clutter to the files, clutter that could have been in it's own place. We'll move all those event arg to their own files.
* We'll also move `IDirectKeyListener` to its own file while we're at it.
* We'll update some of `TermControl`'s old `DEFINE`/`DECLARE_TYPED_EVENT` macros to the newer `TYPED_EVENT` macro, which is a bit nicer.
* We'll change `TermControl.TitleChanged` to a typed event. I needed that for a future PR, so let's just do it here
* While we're updating `TYPED_EVENT` macros, let's do `TerminalPage` too.
### checklist
* [x] I work here
* [x] This is work for #1256, but we've got a long way to go before that works.
