[Java.Interop.Tools.Cecil] Change DirectoryAssemblyResolver Warning to Diagnostic Output (#622)

Context: dotnet/android#2120

When building an app and using an Obfuscator you wind up with a lot
of warnings such as:

	warning : Failed to read 'obj\Release\90\android\assets\DotfuscatorForms.Android.dll' with debugging symbols. Retrying to load it without it. Error details are logged below.
	warning : Mono.Cecil.Cil.SymbolsNotMatchingException: Symbols were found but are not matching the assembly

These are probably the result of the Obfuscation process since the
assembly changed.  However the warning was *not* useful or -- more
importantly -- actionable by the user.  It is just noise.  It might
be useful for the developers writing the Java.Interop tooling itself.

Rather than a warning, change the message to be `Verbose`. This will
allow it up show up in full diagnostic output, but NOT in a normal
build.  It won't be a warning so users will not feel a need to fix it.

Author: dellis1972

src/Java.Interop.Tools.Cecil/Java.Interop.Tools.Cecil/DirectoryAssemblyResolver.cs

@@ -163,9 +163,9 @@ protected virtual AssemblyDefinition ReadAssembly (string file)
 				return AssemblyDefinition.ReadAssembly (file, reader_parameters);
 			} catch (Exception ex) {
 				logger (
-						TraceLevel.Warning,
+						TraceLevel.Verbose,
 						$"Failed to read '{file}' with debugging symbols. Retrying to load it without it. Error details are logged below.");
-				logger (TraceLevel.Warning, $"{ex.ToString ()}");
+				logger (TraceLevel.Verbose, $"{ex.ToString ()}");
 				reader_parameters.ReadSymbols = false;
 				return AssemblyDefinition.ReadAssembly (file, reader_parameters);
 			}