"echo" is an uncommon term and the action is most commonly referred
to as a "repeated" key press.
This also improves the documentation related to echo behavior.
We don't use that info for anything, and it generates unnecessary diffs
every time we bump the minor version (and CI failures if we forget to
sync some files from opt-in modules (mono, text_server_fb).
The `InputEvent` class currently supports the `pressed` and `released` states, which given the binary nature, is represented by a `bool` field.
This commit introduced the `CANCELED` state, which signals that an ongoing input event has been canceled.
To represent all the states, the `InputEventState` enum is added and the `InputEvent` logic is refactored accordingly.
This makes it easier to spot syntax errors when editing the
class reference. The schema is referenced locally so validation
can still work offline.
Each class XML's schema conformance is also checked on GitHub Actions.
For the time being we don't support writing a description for those, preferring
having all details in the method's description.
Using self-closing tags saves half the lines, and prevents contributors from
thinking that they should write the argument or return documentation there.