Ruffle does not allow keyboard navigation keys to work

[Lord-McSweeney]

Currently, Ruffle traps CTRL+R, Tab, Page Down, and Page Up. In addition, the Ruffle container cannot be accessed by Tabbing to it (fixable by setting tabindex="0" on the Ruffle container). The keys being trapped present a nuisance to keyboard-focused users. In Flash, fscommand has the trapallkeys function, which helped, but fscommand's functions are unimplemented in Ruffle.

[danielhjacobs]

Worth noting, if the tab key behavior of the original Flash player is ever implemented, it would probably be necessary for Ruffle to trap tab key clicks (#5443).