Fire an event during font discovery to allow for wiring in font redirects and lazy loading

[tocsoft]

add an event to IFontCollection that will be called before a font instance is returned that can be used to switch the font instance in the collection with an alternative one.

Additionally should be able to register a new font file during this callback and allow the newly installed file to be returned in place of discovered instance.

public class FontDiscoveryEventArgs : EventArgs
{
    public string FontName { get; }
    public FontStyle FontStyle { get; }
    public bool FontFamilyInstalled { get; }
    public bool FontInstalled { get; }

    public bool UseFont(string path){
       //  .. calls font collection install and then sets the font name and style to the installed font returned
    }

    public bool UseFont(Stream stream){
       //  .. calls font collection install and then sets the font name and style to the installed font returned
    }

    public bool UseFont(string fontName, FontStyle style){
        // tries to find the font in the collection if exists then it replaces the final 
        // returned font with the newly named one and returns true.
        //if doesn't exist then no change and returns false
    }
}

if after the event is called we still don't have a matching font then we will follow the same logic we have now and ultimately throw as required.