Fix duplicate attributes defined in Spinner and TextAppearance attrs.xml

[alexeystrakh]

When I'm trying to bind the material .aar library with Xamarin.Android, tooling raises an error:

../obj/Debug/android/src/com/rey/material/R.java(27,27): Error JAVAC0000:  error: variable Spinner_android_dropDownWidth is already defined in class styleable
public static final int Spinner_android_dropDownWidth = 6;

After a quick research, I figured out that the rey5137/material defines styleable attributes with reserved by Android SDK names. You can see it by hovering that attribute. And while this is just a warning in Android Studio, it's a blocker error in Xamarin.Android and I'm unable to bind this library:

I'm not very familiar with styleable attributes but after some reading it seems that we want to define new attributes with unique names and move the rest into a common section to avoid duplicates. In our case, we also don't want to use reserved attributes names. The following 11 attributes were renamed to avoid that conflict:

1. Spinner_android_dropDownWidth
2. Spinner_android_popupBackground
3. Spinner_android_prompt
4. TextAppearance_android_textColor
5. TextAppearance_android_textColorHint
6. TextAppearance_android_textColorLink
7. TextAppearance_android_textSize
8. TextAppearance_android_typeface
9. TextAppearance_android_fontFamily
10. TextAppearance_android_textStyle
11. TextAppearance_android_shadowColor
12. TextAppearance_android_shadowDx
13. TextAppearance_android_shadowDy
14. TextAppearance_android_shadowRadius