Make it possible to set languages defined by an extension as default …

[marcelgerber]

…for a file extension

Filtering out languages which are not currently defined (because they are probably defined by an extension later on) fixes the case described in #11252.

[Already done] Currently, it seems to be working miraculously as the pref change handler fires late enough, but I think I should add an additional AppInit.extensionsLoaded callback just to be safe. (Does anyone know why the change handler is called so late? I don't think that's the intended behavior...)

[TomMalbran]

Should we consider the case of a language being defined after the extensions are loaded? Might happen if an extension defines a language after some sort of action and not at startup, or maybe you could have installed a language, set it as default, then deleted that extension, restarted brackets, waited a bit and reinstalled the same language extension.

[marcelgerber]

I've thought about that too, but I didn't consider the case of installing a new extension.
I'll change it to be updated on defineLanguage soon.

[TomMalbran]

I was thinking to call the update code if the preference manager is defined every time a new language is defined.

[marcelgerber]

@TomMalbran Did that as well.
Unfortunately, I had to move the code around as JSLint had complained otherwise.

[marcelgerber]

Superseded by #12979.
Closing.