[marshal methods] Properly support arrays of arrays

[grendello]

Fixes: #7693

Java code similar to:

package com.xamarin.android;

public interface DataListener {
  void onDataReceived (
    java.lang.String fromNode,
    java.lang.String fromChannel,
    java.lang.String payloadType,
    byte[][] payload);
}

Generates Java JNI signature:

(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;[[B)V

which then would throw our marshal methods native assembly generator off, because it didn't expect that there might be consecutive [ characters for parameters which are arrays of arrays (of any rank):

System.InvalidOperationException: Unsupported JNI array type '[' at index 56 of signature '(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;[[B)V'
error XAGPM7009:    at Xamarin.Android.Tasks.MarshalMethodsNativeAssemblyGenerator.<ParseJniSignature>g__JniTypeToManaged|55_0(Char jniType, <>c__DisplayClass55_0&)
error XAGPM7009:    at Xamarin.Android.Tasks.MarshalMethodsNativeAssemblyGenerator.ParseJniSignature(String signature, MethodDefinition implementedMethod)
error XAGPM7009:    at Xamarin.Android.Tasks.MarshalMethodsNativeAssemblyGenerator.ProcessAndAddMethod(List`1 allMethods, MarshalMethodEntry entry, Boolean useFullNativeSignature, Dictionary`2 seenClasses, Dictionary`2 overloadedNativeSymbolNames)
error XAGPM7009:    at Xamarin.Android.Tasks.MarshalMethodsNativeAssemblyGenerator.Init()
error XAGPM7009:    at Xamarin.Android.Tasks.GeneratePackageManagerJava.AddEnvironment()
error XAGPM7009:    at Xamarin.Android.Tasks.GeneratePackageManagerJava.RunTask()
error XAGPM7009:    at Microsoft.Android.Build.Tasks.AndroidTask.Execute() in /Users/builder/azdo/_work/1/s/xamarin-android/external/xamarin-android-tools/src/Microsoft.Android.Build.BaseTasks/AndroidTask.cs:line 17

Fix this by skipping over the "extra" [ characters. This generates code which uses a simple pointer to array, instead of a pointer to pointer etc. We can take this shortcut because we don't dereference the parameter in our generated code in any way, instead passing it as-is to the managed code.