RFR: 8243208: Clean up JVMFlag implementation [v4]

[Ioi Lam]

> The initial commit [d85cbd6](https://github.com/openjdk/jdk/commit/d85cbd638f5b87c80eee9a92d10e1ac19d9bb2f8) is the
> same patch as
> [8243208-cleanup-jvmflag-impl.v02](https://cr.openjdk.java.net/~iklam/jdk16/8243208-cleanup-jvmflag-impl.v02/)
> published in
> [hotspot-dev at openjdk.java.net](https://mail.openjdk.java.net/pipermail/hotspot-dev/2020-September/042863.html).  The
> rest of the review will continue on GitHub. I will add new commits to respond to comments to the above e-mail.

Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:

  Refactored JVMFlagLookup::hash_code(); Cleaned up LimitGetter::no_limit()

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/82/files
  - new: https://git.openjdk.java.net/jdk/pull/82/files/10246284..bf90a376

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=82&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=82&range=02-03

  Stats: 24 lines in 2 files changed: 7 ins; 12 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/82.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/82/head:pull/82

PR: https://git.openjdk.java.net/jdk/pull/82