RFR: 8020062: Nest StreamBuilder interfaces inside relevant Stream interfaces

[Henry Jen]

Hi,

Please review the webrev at

http://cr.openjdk.java.net/~henryjen/ccc/8020062/0/webrev/index.html

This webrev does as the bug suggested, is a refactoring that moves
StreamBuilder interfaces implementations into relevant Stream interfaces.

The patch is created against the version after applying two earlier RFR
of 8015315+8019395, which we hope will be pushed before this one. That
said, there is no hard dependency on those two changesets.

Cheers,
Henry