avec l’accessibilité en ligne de mire (lecteurs d'écran)

Accessibility is super important for many reasons I shouldn’t need to repeat.
I put together an implementation of the new GtkAccessibleText for VteTerminal and am bundling it with Ptyxis to get more testing.
Since this has the potential to really overload the screen reader as the final interfaces are figured out, it’s gated behind a toggle in preferences. I also am hesitant to enable it by default until we have a way in the a11y stack to be extremely lazy about initialization. I don’t want to waste a lot of CPU cycles tracking changes only for them to be sent to an accessibility D-Bus where nobody is listening.