RFR: 8294137: Review running times of java.math tests [v2]

[Brian Burkhalter]

> Break up `BigIntegerTest` and `SymmetricRangeTests` into subsets which are run quasi-randomly as a function of second within the minute at the time the test is running. `LargeValueExceptions` does not appear amenable to this treatment.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8303269: Use Random instead of Calendar to select test subset

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12819/files
  - new: https://git.openjdk.org/jdk/pull/12819/files/3128f03c..ca998b8e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12819&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12819&range=00-01

  Stats: 10 lines in 2 files changed: 2 ins; 5 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12819.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12819/head:pull/12819

PR: https://git.openjdk.org/jdk/pull/12819