Restructure JSImport/JSExport generators to share more code and utilize more Microsoft.Interop.SourceGeneration shared code (#107769)

Author: jkoritzinsky

src/libraries/System.Runtime.InteropServices.JavaScript/System.Runtime.InteropServices.JavaScript.sln

@@ -14,6 +14,7 @@ internal static class Constants
 
         public const string JSFunctionSignatureGlobal = "global::System.Runtime.InteropServices.JavaScript.JSFunctionBinding";
         public const string JSMarshalerArgumentGlobal = "global::System.Runtime.InteropServices.JavaScript.JSMarshalerArgument";
+        public const string JSMarshalerArgument = "System.Runtime.InteropServices.JavaScript.JSMarshalerArgument";
         public const string ModuleInitializerAttributeGlobal = "global::System.Runtime.CompilerServices.ModuleInitializerAttribute";
         public const string CompilerGeneratedAttributeGlobal = "global::System.Runtime.CompilerServices.CompilerGeneratedAttribute";
         public const string DynamicDependencyAttributeGlobal = "global::System.Diagnostics.CodeAnalysis.DynamicDependencyAttribute";