RFR: Classfile signature bang support [v2]

[Chen Liang]

> Support parsing ! signatures in ClassFile API.

Chen Liang 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 three additional commits since the last revision:

 - Review, various cleanup
 - Merge branch 'bworld' of https://github.com/openjdk/valhalla into feature/cf-bang-sig
 - Classfile signature bang support

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1933/files
  - new: https://git.openjdk.org/valhalla/pull/1933/files/b256fe21..335464c6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1933&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1933&range=00-01

  Stats: 211 lines in 11 files changed: 164 ins; 2 del; 45 mod
  Patch: https://git.openjdk.org/valhalla/pull/1933.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1933/head:pull/1933

PR: https://git.openjdk.org/valhalla/pull/1933