class KeyEventInjector

Provides the ability to inject `KeyEvent`s into the keyboard subsystem.

# Roles

This protocol will typically be:

* Implemented by platform components which process and deliver keyboard

events.

* Consumed by components which originiate keyboard events. E.g.

an on-screen keyboard, or the Session Framework Input Pipeline.

# Related protocols

This protocol should be using in preference to legacy protocols which provide

similar functionality. Specifically, this means this protocol should be preferred

over

* `fuchsia.ui.input.ImeService` which provides `InjectInput()`, `DispatchKey()`,

and `DispatchKey3()`

* `fuchsia.ui.input.InputMethodEditor`, which provides `InjectInput()` and

`DispatchKey3()`

# Notes

Products should take care to limit access to this protocol, as events injected

with this protocol are indistinguishable from those coming from physical devices.