Figure out how to handle the fallback if fonts are not present in jdk-home/lib/fonts directory

The fallback mentioned in Summary is already handled in JavaFX. It needs a closer look to see if things can be improved especially in case when using with OpenJDK.

This has two parts-
1) To support running OpenJFX against OpenJDK which does not have Lucida Sans Fonts then we need to look at the caller of getJDKFontDir() and see whether it makes sense to remove the call as we know upfront these fonts are not supported by OpenJDK.

2) Consider using "System" as a preferred way of finding fonts.
Note : We need to make sure we don't have a circularity in the case that we are using this in initializing System.


Also, as noted in a review comment on JDK-8195806, in method getJDKFontDir() of class PrismFontFactory, please check whether the returned string needs a File.separator at the end.