RFR: 8292758: put support for UNSIGNED5 format into its own header file [v2]

[John R Rose]

> Refactor code from inside of CompressedStream into its own unit.
> 
> This code is likely to be used in future refactorings, such as JDK-8292818 (replace 96-bit representation for field metadata with variable-sized streams).
> 
> Add gtests.

John R Rose 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' of https://git.openjdk.org/jdk into compressed-stream
 - 8292758: put support for UNSIGNED5 format into its own header file

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/10067/files
  - new: https://git.openjdk.org/jdk/pull/10067/files/e938b018..d903f2c7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10067&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10067&range=00-01

  Stats: 9272 lines in 306 files changed: 2846 ins; 5909 del; 517 mod
  Patch: https://git.openjdk.org/jdk/pull/10067.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10067/head:pull/10067

PR: https://git.openjdk.org/jdk/pull/10067