include ExplicitConstructorAttribute's targets to constructor&method (#1982)

* add method target for explicitconstructor

* add a noting comment (usage is limited with Dapper.AOT)

Author: DeagleGross

Dapper/ExplicitConstructorAttribute.cs

@@ -5,7 +5,10 @@ namespace Dapper
     /// <summary>
     /// Tell Dapper to use an explicit constructor, passing nulls or 0s for all parameters
     /// </summary>
-    [AttributeUsage(AttributeTargets.Constructor, AllowMultiple = false)]
+    /// <remarks>
+    /// Usage on methods is limited to the usage with Dapper.AOT (https://github.com/DapperLib/DapperAOT)
+    /// </remarks>
+    [AttributeUsage(AttributeTargets.Constructor | AttributeTargets.Method, AllowMultiple = false)]
     public sealed class ExplicitConstructorAttribute : Attribute
     {
     }