rework SymbolFactory

- rename & move to Pilz.UI..Telerik.Symbols.RadSymbolFactory
- make default implementaiton available at Pilz.UI.Symbols.SymbolFactory
- add interfaces

Pilz.UI/Symbols/SymbolSize.cs

@@ -0,0 +1,21 @@
+namespace Pilz.UI.Symbols;
+
+public enum SymbolSize
+{
+    /// <summary>
+    /// Don't resize and just returns the original size.
+    /// </summary>
+    Default,
+    /// <summary>
+    /// Resizes the symbol to 16 x 16 pixels.
+    /// </summary>
+    Small,
+    /// <summary>
+    /// Resizes the symbol to 20 x 20 pixels.
+    /// </summary>
+    Medium,
+    /// <summary>
+    /// Resizes the symbol to 32 x 32 pixels.
+    /// </summary>
+    Large
+}