RFR: 8318827: RISC-V: Improve readability of fclass result testing [v3]

[Feilong Jiang]

> Hi, please consider.
> 
> Currently, we test results of `fclass` instruction with hard-coded bits which has bad readability. This patch adds an enumeration of the flcass mask bits for ease of use.
> 
> Testing:
> 
> - [ ] tier1 with release build

Feilong Jiang 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 four additional commits since the last revision:

 - Merge branch 'master' of https://github.com/openjdk/jdk into riscv-fclass-mask
 - remove 'fclass_' prefix
 - adjust enum name style
 - Add FCLASS_MASK enum for better readability

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16362/files
  - new: https://git.openjdk.org/jdk/pull/16362/files/593913ef..8ffc88a3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16362&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16362&range=01-02

  Stats: 4762 lines in 256 files changed: 2465 ins; 1682 del; 615 mod
  Patch: https://git.openjdk.org/jdk/pull/16362.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16362/head:pull/16362

PR: https://git.openjdk.org/jdk/pull/16362