[crac] RFR: Selectable Global Context implementation

[Anton Kozlov]

A number of problems were caused by switching to BlockingOrderedContext in the JDK code. To prevent the same in the potential users of EA builds, I temporarily switch the default implementation to the previous OrderedContext. The BlockingContext is still available via a command line option. After an EA build and transition of CRaC development to track newer version openjdk/jdk, the default implementation will be changed.

To make properties available, it was required to delay Reference resource registration. Otherwise, the GlobalContext implementation decision had to be done too early, in the Reference initialization during JDK bootstrapping, before Properties are available.

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Commit messages:
 - WIP
 - Selectable Context

Changes: https://git.openjdk.org/crac/pull/87/files
 Webrev: https://webrevs.openjdk.org/?repo=crac&pr=87&range=00
  Stats: 73 lines in 4 files changed: 55 ins; 16 del; 2 mod
  Patch: https://git.openjdk.org/crac/pull/87.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/87/head:pull/87

PR: https://git.openjdk.org/crac/pull/87