Remove Instance property since it is not part of System.Drawing interface and it is only used on FontFamily

Author: cinthamo

src/Common/FontFamily.cs

@@ -326,7 +326,8 @@ public bool IsStyleAvailable(FontStyle style)
 	/// <summary>
 	/// Returns an array that contains all of the <see cref='FontFamily'/> objects of the system
 	/// </summary>
-	public static FontFamily[] Families => InstalledFontCollection.Instance.Families;
+	public static FontFamily[] Families => s_Families ??= new InstalledFontCollection().Families;
+	private static FontFamily[] s_Families; // cache to load the fonts once
 
 	/// <summary>
 	///  Gets a generic monospace <see cref='FontFamily'/>.

src/Common/Text/InstalledFontCollection.cs

@@ -12,8 +12,6 @@ public class InstalledFontCollection : FontCollection
 	private static readonly string SYSTEM_FONT_PATH = Environment.GetFolderPath(Environment.SpecialFolder.Fonts);
 	private static readonly string[] FONT_EXTENSIONS = { ".ttf", ".otf", ".eot", ".woff", ".woff2" };
 
-	public static readonly FontCollection Instance = new InstalledFontCollection();
-	
 	/// <summary>
 	/// Initializes a new instance of the <see cref='InstalledFontCollection'/> class.
 	/// </summary>