[jcw-gen] Use + for ntested types, not /

TODO: full explanation.

#1302 and dotnet/android#9750 has turned into a
bit of a boondoggle.  Maybe the better approach is to just update
`jcw-gen` to use `+` instead of `/` for nested types, instead of
*both* `jcw-gen` *and* `generator`, because the `generator` changes
just require changes *everywhere*.

Will this smaller fix work?

Author: jonpryor

src/Java.Interop.Tools.JavaCallableWrappers/Java.Interop.Tools.JavaCallableWrappers.Adapters/CecilImporter.cs

@@ -269,7 +269,7 @@ static CallableWrapperMethod CreateMethod (MethodDefinition methodDefinition, Ca
 	static CallableWrapperMethod CreateMethod (string name, CallableWrapperType declaringType, string? signature, string? connector, string? managedParameters, string? outerType, string? superCall)
 	{
 		signature = signature ?? throw new ArgumentNullException ("`connector` cannot be null.", nameof (connector));
-		var method_name = "n_" + name + ":" + signature + ":" + connector;
+		var method_name = "n_" + name + ":" + signature + ":" + connector?.Replace ('/', '+');
 
 		var method = new CallableWrapperMethod (declaringType, name, method_name, signature);
 

src/Java.Interop.Tools.TypeNameMappings/Java.Interop.Tools.TypeNameMappings/JavaNativeTypeManager.cs

@@ -150,7 +150,7 @@ static string ToCliTypePart (string part)
 			for (int i = 0; i < parts.Length; ++i) {
 				parts [i] = ToPascalCase (parts [i], 1);
 			}
-			return string.Join ("/", parts);
+			return string.Join ("+", parts);
 		}
 
 		static string ToPascalCase (string value, int minLength)