RFR: JDK-8296322 javac: use methods to manage parser mode flags [v2]

[Jim Laskey]

> Manage parser mode flags using methods for easy of reading and maintenance.

Jim Laskey 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 two additional commits since the last revision:

 - Merge branch 'master' into 8296322
 - JDK-8296322 javac: use methods to manage parser mode flags

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10981/files
  - new: https://git.openjdk.org/jdk/pull/10981/files/cc0989c0..faf18a62

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10981&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10981&range=00-01

  Stats: 260808 lines in 5800 files changed: 125648 ins; 81789 del; 53371 mod
  Patch: https://git.openjdk.org/jdk/pull/10981.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10981/head:pull/10981

PR: https://git.openjdk.org/jdk/pull/10981