[jdk17u-dev] RFR: 8290079: Reduce interaction with volatile in static initializer of BigInteger

[Roland Mesde]

Backporting JDK-8290079: Reduce interaction with volatile in static initializer of BigInteger.

```BigInteger.powerCache``` is volatile and should be assigned only once in static initializer.

Ran GHA Sanity Checks (passed) and related test (passed).

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Commit messages:
 - Backport c83fcbd18fff4d10c4162c43ddcdf3a51ce2c8e6

Changes: https://git.openjdk.org/jdk17u-dev/pull/4191/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=4191&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290079
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/4191.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/4191/head:pull/4191

PR: https://git.openjdk.org/jdk17u-dev/pull/4191