RFR: JDK-8222949: add condy support to javac's pool API

[Vicente Romero]

Please review the fix for [1] at [2]. This enhancement is related to [3] 
which introduced a new API for constant pool reading / writing in javac. 
The current patch adds condy support that was missing.

Thanks,
Vicente

[1] https://bugs.openjdk.java.net/browse/JDK-8222949
[2] http://cr.openjdk.java.net/~vromero/8222949/webrev.00/
[3] https://bugs.openjdk.java.net/browse/JDK-8222289