RFR: 8166365: Small immutable collections should provide optimized implementations when possible

[Claes Redestad]

Hi,

please review this change to improve startup/warmup characteristics
and performance of the immutable collection factories:

Bug: https://bugs.openjdk.java.net/browse/JDK-8166365
Webrev: http://cr.openjdk.java.net/~redestad/8166365/webrev.01/

While filed as an RFE, and a more thorough examination of the hierarchy
of the ImmutableCollection classes has been discussed[1], this more
limited patch resolves some immediate issues related to module system
bootstrap and is therefore motivated to push to 9.

Thanks!

/Claes

[1] we should likely not inherit Iterator classes that check for
co-modification etc,