RFR: 6899: Upgrade core to 8 [v2]

[Marcus Hirt]

> For some reason the Eclipse compiler fails some type inferences when switching to JDK 8, so had to add some
> (unnecessary) casts. (Also set JDK 11 as required for running the application builds.)

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/120/files
  - new: https://git.openjdk.java.net/jmc/pull/120/files/96e10707..bcc22b6a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=120&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=120&range=00-01

  Stats: 23 lines in 2 files changed: 0 ins; 0 del; 23 mod
  Patch: https://git.openjdk.java.net/jmc/pull/120.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/120/head:pull/120

PR: https://git.openjdk.java.net/jmc/pull/120