RFR: 6899: Upgrade core to 8 [v3]

[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:

  Fixing copyright year

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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/bcc22b6a..04466fb7

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=120&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=120&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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