RFR: JDK-8173605: Remove support for source and target 1.7 option in javac [v2]

[Joe Darcy]

> Update to remove support for -source/-target/--release 7 from javac.
> 
> As seen in the PR, many test fails are affected. Further refactorings of javac's implementation that can be made from dropping 7 support are left as future work.

Joe Darcy has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 27 additional commits since the last revision:

 - Update copyrights.
 - Delete unneeded test.
 - Merge branch 'master' into JDK-8173605
 - Merge branch 'master' into JDK-8173605
 - Small refactoring to remove more stale code.
 - Remove effectively dead code.
 - Adjust data for CheckExamples test.
 - Partial restore of DEFAULT_METHODS Source.Feature for test java/lang/invoke/defineHiddenClass/PreviewHiddenClass.java.
 - Merge branch 'master' into JDK-8173605
 - Fix MultiReleaseJars.java.
 - ... and 17 more: https://git.openjdk.org/jdk/compare/a81a20ee...b2039d68

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/10074/files
  - new: https://git.openjdk.org/jdk/pull/10074/files/f3095350..b2039d68

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10074&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10074&range=00-01

  Stats: 14641 lines in 536 files changed: 4475 ins; 7382 del; 2784 mod
  Patch: https://git.openjdk.org/jdk/pull/10074.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10074/head:pull/10074

PR: https://git.openjdk.org/jdk/pull/10074