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

[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.

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Commit messages:
 - 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.
 - Test fixes.
 - Clean langtools test run.
 - CheckExamples passes.
 - Type annotations.
 - ... and 13 more: https://git.openjdk.org/jdk/compare/76ee5495...f3095350

Changes: https://git.openjdk.org/jdk/pull/10074/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10074&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8173605
  Stats: 4514 lines in 156 files changed: 25 ins; 4362 del; 127 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