Added support for shared libraries in AARs.

AAR support in Unity varies by version and build system, this patch
adds support for shared libraries (.so) files in AARs using a variety
of methods:
* Unity 4:
  - Internal (default) build system
    Shared libraries in the jni folder of AARs are supported but the
    "jni" folder is ignored when AARs are expanded / exploded so this
    copies shared libraries to the "lib" folder in the expanded AAR
    where they're included in the built APK.
* Unity <= 5.4
  - Internal (default) build system
    Similar behavior as Unity 4 except only AARs with shared libs or
	that require variable expansion are exploded.
* Unity 5.5
  - Internal (default) build system
    Same behavior as Unity 5.4
  - Gradle / Android Studio
    Settings dialog can disable expansion / explosion of AARs as
	they're supported natively by the Android Gradle build system.
	The settings dialog is required to configure this behavior as
	Unity does not set the applicationId variable in the generated
	build.gradle.

In addition:
* Enabled the Android Resolver settings dialog when any platform is
  selected.
* Made it possible to configure the target folder for AARs / exploded
  AAR directories.  Though this turned up a bug in Unity's Android
  library search process which fails to find libraries in subdirectories
  so the functionality is disabled at the moment.

googlesamples#34
googlesamples#29

BUG=34667843

Change-Id: I843b89ffa614ee2b3508c0a9e0e8a6c025a1668c

Author: Stewart Miles

source/JarResolverLib/src/Google.JarResolver/Dependency.cs

@@ -32,6 +32,16 @@ namespace Google.JarResolver
     /// </summary>
     public class Dependency
     {
+        // TODO(wilkinsonclay): get the extension from the pom file.
+        internal static string[] Packaging = {
+            ".aar",
+            ".jar",
+            // This allows users to place an aar inside a Unity project and have Unity
+            // ignore the file as part of the build process, but still allow the Jar
+            // Resolver to process the AAR so it can be included in the build.
+            ".srcaar"
+        };
+
         /// <summary>
         /// The version comparator.  This comparator results in a descending sort
         /// order by version.
@@ -64,8 +74,14 @@ public Dependency(string group, string artifact, string version, string[] packag
             PackageIds = packageIds;
             this.possibleVersions = new List<string>();
             Repositories = repositories;
+            CreatedBy = System.Environment.StackTrace;
         }
 
+        /// <summary>
+        /// Stack trace of the point where this was created.
+        /// </summary>
+        internal string CreatedBy { get; private set; }
+
         /// <summary>
         /// Gets the group ID
         /// </summary>
@@ -153,6 +169,25 @@ public string BestVersionPath
             }
         }
 
+        /// <summary>
+        /// Get the path to the artifact.
+        /// </summary>
+        public string BestVersionArtifact
+        {
+            get
+            {
+                // TODO(wilkinsonclay): get the extension from the pom file.
+                string filenameWithoutExtension =
+                    Path.Combine(BestVersionPath, Artifact + "-" + BestVersion);
+                foreach (string extension in Packaging)
+                {
+                    string filename = filenameWithoutExtension + extension;
+                    if (File.Exists(filename)) return filename;
+                }
+                return null;
+            }
+        }
+
         /// <summary>
         /// Gets or sets the repository path for this dependency.  This is
         /// relative to the SDK.