Implement feature to use game resource fonts

Dalamud/Interface/GameFonts/GameFontHandle.cs

@@ -0,0 +1,35 @@
+using System;
+
+using ImGuiNET;
+
+namespace Dalamud.Interface.GameFonts
+{
+    /// <summary>
+    /// Prepare and keep game font loaded for use in OnDraw.
+    /// </summary>
+    public class GameFontHandle : IDisposable
+    {
+        private readonly GameFontManager manager;
+        private readonly GameFont font;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="GameFontHandle"/> class.
+        /// </summary>
+        /// <param name="manager">GameFontManager instance.</param>
+        /// <param name="font">Font to use.</param>
+        internal GameFontHandle(GameFontManager manager, GameFont font)
+        {
+            this.manager = manager;
+            this.font = font;
+        }
+
+        /// <summary>
+        /// Gets the font.
+        /// </summary>
+        /// <returns>Corresponding font or null.</returns>
+        public ImFontPtr? Get() => this.manager.GetFont(this.font);
+
+        /// <inheritdoc/>
+        public void Dispose() => this.manager.DecreaseFontRef(this.font);
+    }
+}