RFR 8171380: Remove exports from jdk.jlink

[Chris Hegarty]

> On 17 Jan 2017, at 00:02, Remi Forax <forax at univ-mlv.fr> wrote:
> 
> Cris,
> it seems that there is a mechanism for API that are experimental in the jdk,
> by example java.net.http uses this mechanism, is it possible to reuse the same mechanism for the jlink plugin API ?

I did look at the possibility exposing the JLink Plugin API through
an incubator module, but found that it would add complication to
the code in order to refactor out the API to the extent where regular
plugins could co-exist with custom plugins, while not having the
jlink module depend on the incubator module. I discussed this 
offline with the jlink folk and they seemed to think that since this
is a niche area, having to add --add-exports to was a reasonable
compromise at this point, rather than the potentially more invasive
changes that would be required to use incubator modules.

-Chris.