Update ProductInfo to use semver-compliant AssemblyInformationalVersion

ProductInfo.ToString() was recently updated to get the assembly version programmatically, instead of using a hard-coded string. But the particular API used--`Assembly.GetName().Version.ToString(3)`--isn't fully compatible with semver. Specifically, it doesn't handle pre-release labels which can extend the MAJOR.MINOR.PATCH format.

This change updates ToString() to use `Assembly.GetCustomAttribute<AssemblyInformationalVersionAttribute>().InformationalVersion`. The InformationalVersion on the assembly holds the semver-compatible version string.

Author: damonbarry

iothub/device/src/ProductInfo.cs

@@ -14,7 +14,7 @@ internal class ProductInfo
         public override string ToString()
         {
             const string Name = "Microsoft.Azure.Devices.Client";
-            string version = typeof(DeviceClient).GetTypeInfo().Assembly.GetName().Version.ToString(3);
+            string version = typeof(DeviceClient).GetTypeInfo().Assembly.GetCustomAttribute<AssemblyInformationalVersionAttribute>().InformationalVersion;
             string runtime = RuntimeInformation.FrameworkDescription.Trim();
             string operatingSystem = RuntimeInformation.OSDescription.Trim();
             string processorArchitecture = RuntimeInformation.ProcessArchitecture.ToString().Trim();