add bunch of new java APIs: mostly stubs or copied from AOSP

Many of these classes are only needed to be subclassed by androidx
support library, which is used in many android apps

src/api-impl/android/widget/Button.java

@@ -0,0 +1,17 @@
+package android.widget;
+
+import android.content.Context;
+import android.util.AttributeSet;
+import android.view.View;
+
+public class Button extends View {
+
+	public Button(Context context) {
+		super(context);
+	}
+
+	public Button(Context context, AttributeSet attributeSet) {
+		super(context, attributeSet);
+	}
+
+}