RFR: First refactoring (thaw_fast) [v4]

[Frederic Parain]

> Refactoring method thaw_fast() for better encapsulation and readability.

Frederic Parain 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 five additional commits since the last revision:

 - Merge remote-tracking branch 'upstream/fibers' into renaming1
 - Merge remote-tracking branch 'upstream/fibers' into renaming1
 - Move new methods to ThawBase
 - Fixes to address Coleen's comments.
 - First refactoring (thaw_fast)

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

Changes:
  - all: https://git.openjdk.java.net/loom/pull/158/files
  - new: https://git.openjdk.java.net/loom/pull/158/files/ecb1109e..5470e42e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=loom&pr=158&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=loom&pr=158&range=02-03

  Stats: 24147 lines in 1149 files changed: 16058 ins; 4200 del; 3889 mod
  Patch: https://git.openjdk.java.net/loom/pull/158.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/158/head:pull/158

PR: https://git.openjdk.java.net/loom/pull/158