Xml Language Extension and TagSynchronization

Hey,

I made a custom language

public class MiniMessageLanguage extends Language {
    private MiniMessageLanguage() {
        this(XMLLanguage.INSTANCE, "MiniMessage");
    }
}

I also implemented the XmlExtension extension point and the XmlTypedHandlersAdditionalSupport extension point.

public class MiniMessageHandlersAdditionalSupport implements XmlTypedHandlersAdditionalSupport {
    @Override
    public boolean isAvailable(@NotNull PsiFile psiFile, @NotNull Language language) {
        return language.isKindOf(MiniMessageLanguage.INSTANCE);
    }
}

However, tag synchronization and typed handlers don't work in MiniMessage files.
When additionally extending XmlLanguage in MiniMessageLanguage, both tag synchronization and typed handlers work. Then however, my XmlExtension method isValidTagNameChar will no longer be called from XmlTag.setName("#123123").

Also I noticed that tag synchronization never works in injected XML. This should maybe be reported.