[Xamarin.Android.Tools.AndroidSdk] Update SDK component for API-30 (#99)

Context: https://dl-ssl.google.com/android/repository/repository2-1.xml

Update the preferred Android SDK component versions to the current latest
versions listed in the [Android Repository file][0]:

  * `$(AndroidSdkBuildToolsVersion)`/build-tools to 30.0.2
  * `$(AndroidCommandLineToolsVersion)`/cmdline-tools to 2.1
  * `$(AndroidSdkPlatformToolsVersion)`/platform-tools to 30.0.4
  * `$(AndroidSdkPlatformVersion)`/platform to android-30
  * `$(AndroidNdkVersion)`/NDK to 21.3.6528147

[0]: https://dl-ssl.google.com/android/repository/repository2-1.xml

Author: jonpryor

src/Xamarin.Android.Tools.AndroidSdk/Xamarin.Android.Tools.Versions.props

@@ -9,12 +9,12 @@
     If this file is changed the submodule for androidtools should be updated, 
     along with any other repo which references androidtools. 
     -->
-    <AndroidSdkBuildToolsVersion Condition="'$(AndroidSdkBuildToolsVersion)' == ''">29.0.2</AndroidSdkBuildToolsVersion>
-    <AndroidCommandLineToolsVersion Condition=" '$(AndroidCommandLineToolsVersion)' == '' ">1.0</AndroidCommandLineToolsVersion>
-    <AndroidSdkPlatformToolsVersion Condition="'$(AndroidSdkPlatformToolsVersion)' == ''">29.0.5</AndroidSdkPlatformToolsVersion>
+    <AndroidSdkBuildToolsVersion Condition="'$(AndroidSdkBuildToolsVersion)' == ''">30.0.2</AndroidSdkBuildToolsVersion>
+    <AndroidCommandLineToolsVersion Condition=" '$(AndroidCommandLineToolsVersion)' == '' ">2.1</AndroidCommandLineToolsVersion>
+    <AndroidSdkPlatformToolsVersion Condition="'$(AndroidSdkPlatformToolsVersion)' == ''">30.0.4</AndroidSdkPlatformToolsVersion>
     <AndroidSdkToolsVersion Condition="'$(AndroidSdkToolsVersion)' == ''">26.1.1</AndroidSdkToolsVersion>
     <AndroidSdkEmulatorVersion Condition="'$(AndroidSdkEmulatorVersion)' == ''"></AndroidSdkEmulatorVersion>
-    <AndroidSdkPlatformVersion Condition="'$(AndroidSdkPlatformVersion)' == ''">android-29</AndroidSdkPlatformVersion>
-    <AndroidNdkVersion Condition="'$(AndroidNdkVersion)' == ''">16.1</AndroidNdkVersion>
+    <AndroidSdkPlatformVersion Condition="'$(AndroidSdkPlatformVersion)' == ''">android-30</AndroidSdkPlatformVersion>
+    <AndroidNdkVersion Condition="'$(AndroidNdkVersion)' == ''">21.3.6528147</AndroidNdkVersion>
   </PropertyGroup>
 </Project>