Android: Automatically download SDK tools and essential packages

Automatically download Android SDK Tools to default path
used by Android Studio, then essential packages will be installed
using the sdkmanager tool. Automatic installation can also be
triggered by an added button in the settings page.

Essentials packages include NDK Bundle and other NDK versions
required by previous Qt versions.

An sdk_definitions.json file holds download paths for SDK Tools,
and other (Qt version <-> essential packages) combinations.

[ChangeLog][Android] Automatically download SDK Tools, NDKs and
all essential packages for Android builds.

Task-number: QTCREATORBUG-23285
Change-Id: I90e7aafecd017d2bdc959e403711d9d440a6bbb2
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/android/androidsdkpackage.cpp

@@ -294,4 +294,29 @@ AndroidSdkPackage::PackageType ExtraTools::type() const
     return AndroidSdkPackage::ExtraToolsPackage;
 }
 
+Ndk::Ndk(QVersionNumber revision, QString sdkStylePathStr, QObject *parent) :
+    AndroidSdkPackage(revision, sdkStylePathStr, parent)
+{
+}
+
+bool Ndk::isValid() const
+{
+    return installedLocation().exists();
+}
+
+AndroidSdkPackage::PackageType Ndk::type() const
+{
+    return AndroidSdkPackage::NDKPackage;
+}
+
+bool Ndk::isNdkBundle() const
+{
+    return m_isBundle;
+}
+
+void Ndk::setAsNdkBundle(const bool isBundle)
+{
+    m_isBundle = isBundle;
+}
+
 } // namespace Android