[Xamarin.Android.Tools.Bytecode] Ignore empty bv values. (#1107)

Fixes: #1106

Context: https://github.com/devtodev-analytics/android-sdk-2.0/blob/ce131e63414d7e6e870c7276c67636fdcfbbd2eb/DTDAnalytics-android%202.3.3/DTDAnalytics-2.3.3.aar

We started seeing warnings when parsing newer Kotlin metadata
annotations:

	% dotnet class-parse.dll classes.jar
	class-parse: warning: Unable to parse Kotlin metadata on 'Utf8("com/devtodev/analytics/external/DTDLogLevel")': System.FormatException: The input string '' was not in a correct format.
	   at System.Number.ThrowOverflowOrFormatException(ParsingStatus status, ReadOnlySpan`1 value, TypeCode type)
	   at System.Int32.Parse(String s)
	   at Xamarin.Android.Tools.Bytecode.KotlinMetadata.ParseInteger(String value) in …/xamarin/Java.Interop/src/Xamarin.Android.Tools.Bytecode/Kotlin/KotlinMetadata.cs:line 148
	   at Xamarin.Android.Tools.Bytecode.KotlinMetadata.<>c.<ParseVersion>b__26_0(String v) in …/xamarin/Java.Interop/src/Xamarin.Android.Tools.Bytecode/Kotlin/KotlinMetadata.cs:line 122
	   at System.Linq.Enumerable.SelectArrayIterator`2.ToArray()
	   at Xamarin.Android.Tools.Bytecode.KotlinMetadata.ParseVersion(Annotation annotation, String key) in …/xamarin/Java.Interop/src/Xamarin.Android.Tools.Bytecode/Kotlin/KotlinMetadata.cs:line 122
	   at Xamarin.Android.Tools.Bytecode.KotlinMetadata.FromAnnotation(Annotation annotation) in …/xamarin/Java.Interop/src/Xamarin.Android.Tools.Bytecode/Kotlin/KotlinMetadata.cs:line 30
	   at Xamarin.Android.Tools.Bytecode.KotlinFixups.Fixup(IList`1 classes) in …/xamarin/Java.Interop/src/Xamarin.Android.Tools.Bytecode/Kotlin/KotlinFixups.cs:line 23

This is because the `bv` entry is set to an empty byte array instead
of an empty string, and we are trying to parse its contents as an
integer array: `bv: []`.

Looking at the [Kotlin source][0], they [decided to deprecate][1] the
`bv` value, and it may no longer be supplied:

	/**
	 * The version of the bytecode interface (naming conventions, signatures) of the class file annotated with this annotation.
	 */
	@deprecated(
	    "Bytecode version had no significant use in Kotlin metadata and it will be removed in a future version.",
	    level = DeprecationLevel.WARNING,
	)
	@get:JvmName("bv")
	val bytecodeVersion: IntArray = [1, 0, 3],

We will just silently ignore a missing `bv` value, since we do not
consume it.

[0]: https://github.com/JetBrains/kotlin/blob/c6d9821ef0746bbbd4c93b7e9c4a2b2468824ce9/libraries/stdlib/jvm/runtime/kotlin/Metadata.kt#L34-L42
[1]: https://youtrack.jetbrains.com/issue/KT-41758

Author: jpobst

src/Xamarin.Android.Tools.Bytecode/Kotlin/KotlinMetadata.cs

@@ -116,7 +116,8 @@ public static KotlinMetadata FromAnnotation (Annotation annotation)
 		{
 			var value = GetValue (annotation, key);
 
-			if (value is null)
+			// Version is missing or empty
+			if (value is null || value == "[]")
 				return null;
 
 			var values = value.Trim ('[', ']').Split (',').Select (v => ParseInteger (v)).ToArray ();