[generator] Handle Java class with base class set to itself.

[jpobst]

Fixes #1031

There apparently exists a Java obfuscator that attempts to break tools by setting the base class of a class to itself. This breaks us with a StackOverflowException:

public class c5<BaseHandler> extends c5<BaseHandler> { ... }

Stack overflow: IP: 0x11ae88918, fault addr: 0x30d984fd8
Stacktrace:
      at Java.Interop.Tools.JavaTypeSystem.Models.JavaClassModel.PrepareGenericInheritanceMapping () [0x00038] in <9ad2a4b0fd014215b74d06fce5575b7a>:0
      <...>
      at Java.Interop.Tools.JavaTypeSystem.Models.JavaClassModel.get_GenericInheritanceMapping () [0x00000] in <9ad2a4b0fd014215b74d06fce5575b7a>:0
      at Java.Interop.Tools.JavaTypeSystem.Models.JavaMethodModel/<>c__DisplayClass47_0.<FindBaseMethod>b__0 (Java.Interop.Tools.JavaTypeSystem.Models.JavaMethodModel) [0x00018] in <9ad2a4b0fd014215b74d06fce5575b7a>:0
      at System.Linq.Enumerable.TryGetFirst<TSource_REF> (System.Collections.Generic.IEnumerable`1<TSource_REF>,System.Func`2<TSource_REF, bool>,bool&) [0x0003f] in <80f7dc36b4e24f4b86610a67568d2e19>:0
      at System.Linq.Enumerable.FirstOrDefault<TSource_REF> (System.Collections.Generic.IEnumerable`1<TSource_REF>,System.Func`2<TSource_REF, bool>) [0x00000] in <80f7dc36b4e24f4b86610a67568d2e19>:0
      at Java.Interop.Tools.JavaTypeSystem.Models.JavaMethodModel.FindBaseMethod (Java.Interop.Tools.JavaTypeSystem.Models.JavaClassModel) [0x00028] in <9ad2a4b0fd014215b74d06fce5575b7a>:0
      at Java.Interop.Tools.JavaTypeSystem.Models.JavaClassModel.ResolveBaseMembers () [0x0002d] in <9ad2a4b0fd014215b74d06fce5575b7a>:0
      at Java.Interop.Tools.JavaTypeSystem.Models.JavaTypeCollection.ResolveCollection (Java.Interop.Tools.JavaTypeSystem.TypeResolutionOptions) [0x001d1] in <9ad2a4b0fd014215b74d06fce5575b7a>:0
      at generator.JavaTypeResolutionFixups.Fixup (string,string,Java.Interop.Tools.Cecil.DirectoryAssemblyResolver,string[]) [0x00055] in <a593e50c39a04879937ed01eece67aa3>:0
      at Xamarin.Android.Binder.CodeGenerator.Run (Xamarin.Android.Binder.CodeGeneratorOptions,Java.Interop.Tools.Cecil.DirectoryAssemblyResolver) [0x00230] in <a593e50c39a04879937ed01eece67aa3>:0
      at Xamarin.Android.Binder.CodeGenerator.Run (Xamarin.Android.Binder.CodeGeneratorOptions) [0x0001b] in <a593e50c39a04879937ed01eece67aa3>:0
      at Xamarin.Android.Binder.CodeGenerator.Main (string[]) [0x0000e] in <a593e50c39a04879937ed01eece67aa3>:0
      at (wrapper runtime-invoke) <Module>.runtime_invoke_int_object (object,intptr,intptr,intptr) [0x0002a] in <a593e50c39a04879937ed01eece67aa3>:0

We can add a check for this scenario to prevent the StackOverflowException and instead remove the offending type. This removal will be logged with other removals in the java-resolution-report.log:

The class '[Class] my.namespace.c5' was removed because the base type 'my.namespace.c5' is invalid.