[foreign] RFR 8211397: consolidate parsing of indentifiers in DescriptorParser

[Maurizio Cimadamore]

Hi,
following the recent parser changes to improve parsing of header 
declarations, this is a followup patch which unifies the parsing logic 
of layout annotation names with the recently introduced logic for 
parsing header declaration names. A new test has been added to check the 
various case of good/bad annotation names.

Webrev:

http://cr.openjdk.java.net/~mcimadamore/panama/8211397/

Cheers
Maurizio