This commit enables passthrough mode for VT Input Mode in ConPty. This
will be used to pass VT Input from Mouse Mode directly to the app on the
other side.

## References
microsoft#545 - VT Mouse Mode (Terminal)
microsoft#376 - VT Mouse Mode (ConPty)

## Detailed Description of the Pull Request / Additional comments

### ConHost
- Set the callback for the InputEngine.
- Retrieve `IsInVirtualTerminalInputMode` from the InputBuffer

### Adapter (Dispatch)
Retrieve `VTInputMode` setting from ConHost

### Parser
- Add a callback to passthrough unknown input sequences directly to the
  input queue.
- If we're in VTInputMode, use the callback

## Validation Steps Performed
Tests should still pass.

## Summary of the Pull Request
Make TerminalControl synthesize mouse events and Terminal send them to
the TerminalInput's MouseInput module.

The implementation here takes significant inspiration from how we handle
KeyEvents.

## References
Closes #545 - VT Mouse Mode (Terminal)
References #376 - VT Mouse Mode (ConPty)

### TerminalControl
- `_TrySendMouseEvent` attempts to send a mouse event via TermInput.
  Similar to `_TrySendKeyEvent`
- Use the above function to try and send the mouse event _before_
  deciding to modify the selection

### TerminalApi
- Hookup (re)setting the various modes to handle VT Input
- Terminal is _always_ in VT Input mode (important for #4856)

### TerminalDispatch
- Hookup (re)setting the various modes to handle VT Input

### TerminalInput
- Convert the mouse input position from viewport position to buffer
  position
- Then send it over to the MouseInput in TerminalInput to actually do it
  (#4848)

## Validation Steps Performed
Tests should still pass.

…e's a problem in Win32 quite yet. (#5208)

## Summary of the Pull Request

When conpty is in VT input mode, we pass through all the input we receive. This includes all the other `Action*Dispatch` methods, but missed this one.

## References
* Missed during #4856 
* Discovered during the course of the #4192 review
* #5205 Also investigated part of the issue, but found a different bug.

## PR Checklist
* [x] Doesn't close anything, just related to above things.
* [x] I work here
* [ ] Tests added/passed
* [n/a] Requires documentation to be updated

## Detailed Description of the Pull Request / Additional comments
This will fix the <kbd>ctrl+alt+space</kbd> in the Terminal thing mentioned in #4192, but doesn't actually resolve the root cause of that bug (which is tracked in #5205).