RFR: 6588: Move JMC core to JDK 8 [v2]

[Marcus Hirt]

> WIP. Now that core requires JDK 8, we can make it a little bit more easygoing when using streams. I'm thinking it would be nice to remove the need for the StreamModel altogether as well.

Marcus Hirt has updated the pull request incrementally with one additional commit since the last revision:

  Formatting

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Changes:
  - all: https://git.openjdk.java.net/jmc/pull/194/files
  - new: https://git.openjdk.java.net/jmc/pull/194/files/819564a6..ac0c6316

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=194&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=194&range=00-01

  Stats: 6 lines in 2 files changed: 0 ins; 3 del; 3 mod
  Patch: https://git.openjdk.java.net/jmc/pull/194.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/194/head:pull/194

PR: https://git.openjdk.java.net/jmc/pull/194