RFR [14] 8235550: Clarify record reflective support specification

[Chris Hegarty]

This is a review request for a change to add a clarification to the
record related core reflection methods, that specifies what it means to
be a record class and access to the record components. Discussed
originally over on amber-spec-experts [1]

I expanded the existing record reflection test and also added a new test
( with the original record push bug no. ) to cover security manager
checks ( since I couldn't find an existing test ).

Bug: https://bugs.openjdk.java.net/browse/JDK-8235550
CSR: https://bugs.openjdk.java.net/browse/JDK-8235583
Webrev: https://cr.openjdk.java.net/~chegar/8235550/webrev.00/

-Chris.

[1] https://mail.openjdk.java.net/pipermail/amber-spec-experts/2019-December/001840.html