RFR: 8057113: (fs) Path should have a method to obtain the filename extension

[Sebastian Stenzel]

> Am 29.01.2021 um 22:33 schrieb Brian Burkhalter <bpb at openjdk.java.net>:
> 
> The behavior of the proposed method for some example cases is as:
> 
> .              -> 
> ..             -> 
> .a.b           -> b
> ......         -> 
> .....a         -> a
> ....a.b        -> b
> ..foo          -> foo
> test.rb        -> rb
> a/b/d/test.rb  -> rb
> .a/b/d/test.rb -> rb
> foo.           -> 
> test           -> 
> .profile       -> 
> .profile.sh    -> sh
> ..foo          -> foo
> .....foo       -> foo
> .vimrc         -> 
> test.          -> 
> test..         -> 
> test...        -> 
> image.jpg      -> jpg
> music.mp3      -> mp3
> video.mp4      -> mp4
> document.txt   -> txt
> 
> If the specification can be agreed upon, then a test will be added to this PR and a corresponding CSR will be filed.

I would propose to add two more test cases:

foo.tar.gz → gz
foo.bar. →