Get OpenJDK from well-known paths, not just registry (#72)

Context: http://work.azdo.io/735565
Turns Out™ that certain anti-virus programs block or otherwise
mitigate access to various Windows Registry keys. (No idea which
anti-virus, or what the symptoms are; this is just What I've Heard.)
Reduce reliance on the registry by looking for the JDK within the
`%ProgramW6432%\Android\jdk\microsoft_dist_openjdk_*` directories,
in which the `*` suffix is a `System.Version`-parsable value, and
prefer the highest JDK found there.
The Registry value is still preferred, if set.

Author: kdubau

nuget.version

@@ -1 +1 @@
-1.0
+1.1

src/Xamarin.Android.Tools.AndroidSdk/Sdks/AndroidSdkWindows.cs

@@ -134,6 +134,7 @@ IEnumerable<JdkInfo> ToJdkInfos (IEnumerable<string> paths, string locator)
 
 returnToJdkInfos(GetPreferredJdkPaths(),"Preferred Registry")
 .Concat(ToJdkInfos(GetOpenJdkPaths(),"OpenJDK"))
+.Concat(ToJdkInfos(GetKnownOpenJdkPaths(),"Well-known OpenJDK paths"))
 .Concat(ToJdkInfos(GetOracleJdkPaths(),"Oracle JDK"));
 }
 
@@ -163,6 +164,36 @@ private static IEnumerable<string> GetOpenJdkPaths ()
 }
 }
 
+/// <summary>
+/// Locate OpenJDK installations by well known path.
+/// </summary>
+/// <returns>List of valid OpenJDK paths in version descending order.</returns>
+privatestaticIEnumerable<string>GetKnownOpenJdkPaths()
+{
+stringJdkFolderNamePattern="microsoft_dist_openjdk_";
+
+varpaths=newList<Tuple<string,Version>>();
+varrootPaths=newList<string>{
+Path.Combine(Environment.ExpandEnvironmentVariables("%ProgramW6432%"),"Android","jdk"),
+Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ProgramFilesX86),"Android","jdk"),
+};
+
+foreach(varrootPathinrootPaths){
+if(Directory.Exists(rootPath)){
+foreach(vardirectoryNameinDirectory.EnumerateDirectories(rootPath,$"{JdkFolderNamePattern}*").ToList()){
+varversionString=directoryName.Replace($"{rootPath}\\{JdkFolderNamePattern}",string.Empty);
+if(Version.TryParse(versionString,outVersionver)){
+paths.Add(newTuple<string,Version>(directoryName,ver));
+}
+}
+}
+}
+
+returnpaths.OrderByDescending(v =>v.Item2)
+.Where(openJdk =>ProcessUtils.FindExecutablesInDirectory(Path.Combine(openJdk.Item1,"bin"),_JarSigner).Any())
+.Select(openJdk =>openJdk.Item1);
+}
+
 privatestaticIEnumerable<string>GetOracleJdkPaths()
 {
 stringsubkey=@"SOFTWARE\JavaSoft\Java Development Kit";