keyCode is not mapped correctly when capital character is given


v0.15.0 / latest

Firefox native behaviour:


`key` is capitalized according to the active shift, thus such capitalized/UC character must be supported by syn.js

test case:

```
['keypress', 'keydown', 'keyup'].forEach((k) => $('#xxx')[0].addEventListener(k, event => { console.log(event); }));
syn.trigger($('#xxx')[0], 'keyup', {character: 'n'});
syn.trigger($('#xxx')[0], 'keyup', {character: 'N', shiftKey: true});
```

must log both events with non-zero `keyCode`

Start with the issue's syn.trigger test case and inspect the synthetic keyboard-event path that maps character and shiftKey to keyCode. Reproduce both the lowercase and uppercase calls in Firefox or the project test setup; done means each logged keyup event has a non-zero keyCode.

Written by the indexing model from the issue text.