[constables] RFR of constants API

[Brian Goetz]

To be clear: we’re asking for an *API review*. No need to review the code right now, just the API and the specs.  

> On May 1, 2018, at 6:32 PM, Vicente Romero <vicente.romero at oracle.com> wrote:
> 
> Please review also the related CSR: https://bugs.openjdk.java.net/browse/JDK-8202031
> 
> Thanks,
> Vicente
> 
> On 04/27/2018 01:31 PM, Vicente Romero wrote:
>> Hi all,
>> 
>> Please review the current proposal of the constants API, which are nominal descriptor types defined in pkg java.lang.invoke.constant. The code can be found at [1]. This API is being developed in the context of JEP 303: Intrinsics for the LDC and INVOKEDYNAMIC Instructions [2]
>> 
>> Thanks in advance for your comments,
>> Vicente
>> 
>> [1] http://cr.openjdk.java.net/~vromero/constant.api/webrev.00
>> [2] http://openjdk.java.net/jeps/303
>