RFR: First refactoring (thaw_fast)

[Frederic Parain]

Refactoring method thaw_fast() for better encapsulation and readability.

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

Commit messages:
 - First refactoring (thaw_fast)

Changes: https://git.openjdk.java.net/loom/pull/158/files
 Webrev: https://webrevs.openjdk.java.net/?repo=loom&pr=158&range=00
  Stats: 178 lines in 9 files changed: 81 ins; 44 del; 53 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