RFR: Merge jdk:master

[Kevin Rushforth]

Manually merge changes from the `jdk` repo.

Fix up the merge conflict in `.jcheck/conf` by taking the updated list of files to check for whitespace errors from the
jdk and the rest of the file from lanai.

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Commit messages:
 - Merge jdk:master
 - 8253244: Shenandoah: cleanup includes in Shenandoah root processor files
 - 8253207: enable problemlists jcheck's check
 - 6714834: JarFile.getManifest() leaves an open InputStream as an undocumented side effect
 - 8244706: GZIP "OS" header flag hard-coded to 0 instead of 255 (RFC 1952 non-compliance)
 - 8253206: Enforce whitespace checking for additional source files

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - master: https://webrevs.openjdk.java.net/?repo=lanai&pr=101&range=00.0
 - jdk:master: https://webrevs.openjdk.java.net/?repo=lanai&pr=101&range=00.1

Changes: https://git.openjdk.java.net/lanai/pull/101/files
  Stats: 90 lines in 6 files changed: 79 ins; 6 del; 5 mod
  Patch: https://git.openjdk.java.net/lanai/pull/101.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/101/head:pull/101

PR: https://git.openjdk.java.net/lanai/pull/101