Make Pickers inherit from AppCompatDialogFragment

AppCompatDialogFragment inherits from DialogFragment, so this is not an API breaking change.
However, styling of AppCompatDialogFragments works slightly different, so we should put a disclaimer in the release notes.
The main advantage is that "dialogCornerRadius" is now correctly applied (previously only the API 28 attribute "android:dialogCornerRadius" would work)
Fixes #588
Fixes #504

Author: wdullaer

library/src/main/java/com/wdullaer/materialdatetimepicker/date/DatePickerDialog.java

@@ -28,7 +28,7 @@
 import androidx.annotation.ColorInt;
 import androidx.annotation.NonNull;
 import androidx.annotation.StringRes;
-import androidx.fragment.app.DialogFragment;
+import androidx.appcompat.app.AppCompatDialogFragment;
 import androidx.core.content.ContextCompat;
 import androidx.core.content.res.ResourcesCompat;
 import android.text.format.DateFormat;
@@ -59,7 +59,7 @@
 /**
  * Dialog allowing users to select a date.
  */
-public class DatePickerDialog extends DialogFragment implements
+public class DatePickerDialog extends AppCompatDialogFragment implements
         OnClickListener, DatePickerController {
 
     public enum Version {

library/src/main/java/com/wdullaer/materialdatetimepicker/time/TimePickerDialog.java

@@ -31,7 +31,7 @@
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.annotation.StringRes;
-import androidx.fragment.app.DialogFragment;
+import androidx.appcompat.app.AppCompatDialogFragment;
 import androidx.core.content.ContextCompat;
 import androidx.core.content.res.ResourcesCompat;
 import android.util.Log;
@@ -61,7 +61,7 @@
 /**
  * Dialog to set a time.
  */
-public class TimePickerDialog extends DialogFragment implements
+public class TimePickerDialog extends AppCompatDialogFragment implements
         OnValueSelectedListener, TimePickerController {
     private static final String TAG = "TimePickerDialog";
 
@@ -258,6 +258,7 @@ public void setTitle(String title) {
         mTitle = title;
     }
 
+    @SuppressWarnings("unused")
     public String getTitle() {
         return mTitle;
     }

sample/src/main/res/values/styles.xml

@@ -8,6 +8,7 @@
         <item name="colorAccent">#ff4081</item>
         <!-- Customize picker mode here. -->
         <item name="mdtp_theme_dark">true</item>
+        <item name="dialogCornerRadius">10dp</item>
     </style>
 
 </resources>