This PR fixes a couple of issues with TSFInputControl alignment:
1. The emoji picker IME in particular would show up overlapping the
current buffer row because I stupidly didn't realize that
`TextBlock.ActualHeight` is 0 right after initialization and before
it has any text. So, the emoji picker will show up on the bottom of
the 0 height TextBlock, which overlaps the current buffer row. This
isn't a problem with CJK because inputting text _causes_ the IME to
show up, so by the time the IME shows up, the TextBlock has text and
accordingly has a height.
2. It turns out the emoji picker IME doesn't follow the `TextBlock`
bottom, unlike Chinese and Japanese IME, so if a user were to compose
near the edge of the screen and let the `TextBlock` start line
wrapping, the emoji IME doesn't follow the bottom of the `TextBlock`
as it grows. This means that the `TextBlock` position doesn't update
in the middle of composition, and the `LayoutRequested` event that it
fires at the beginning of composition is the only chance we get to
tell the emoji IME where to place itself. It turns out when we reset
`TextBlock.Text`, the ActualHeight doesn't get immediately reset back
to the min size. So if a user were to bring up the emoji IME before
`ActualHeight` is reset, the IME will show up way below the current
buffer row.
3. We don't currently `TryRedrawCanvas` when the window position changes
(resizing, dragging the window around), so sometimes dragging or
resizing the Terminal doesn't update the position of the IME. Ideally
it should be listening to some "window position changed" event, but
alas we don't have that and it would be much harder than this
incoming fix. We'll just track the window bounds as part of
`TryRedrawCanvas` and redraw if it changes. For the most part, this
will allow the IME to update to where the new window position is, but
it'll only be called if we receive a `LayoutRequested` event.
## PR Checklist
* [x] Closes#5470
* [x] CLA signed.
* [x] Tests added/passed
## Validation Steps Performed
I play with it for quite a bit.
64f8bbf5ff