Tweak FAB sizing method (fixes #2398)

Ref: https://stackoverflow.com/questions/56945314/floating-action-button-fab-icon-size-problems-after-migrating-to-sdk-28

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

@@ -137,8 +137,9 @@
     <style name="Theme.Widget" />
 
     <style name="Theme.Widget.FAB">
-        <item name="android:layout_height">@dimen/fab_size</item>
-        <item name="android:layout_width">@dimen/fab_size</item>
+        <item name="android:layout_height">wrap_content</item>
+        <item name="android:layout_width">wrap_content</item>
+        <item name="fabCustomSize">@dimen/fab_size</item>
         <item name="android:layout_gravity">bottom|end</item>
         <item name="android:layout_margin">@dimen/fab_margin</item>
         <item name="android:scaleType">fitCenter</item>