RFR: 8302987: Add uniform and spatially equidistributed bounded double streams to RandomGenerator [v8]

[Raffaello Giulietti]

> The `default` method `nextDouble(double origin, double bound)` in `java.util.random.RandomGenerator` aims at generating a uniformly and spatially equidistributed random `double` in the left-closed and right-open range [`origin`, `bound`). It does so by applying the affine transform `origin + (bound - origin) * r` to a uniformly and spatially equidistributed random `double` `r` in the range [0, 1).
> 
> Since floating-point arithmetic suffers from small but noticeable rounding errors, this ends up slightly deforming the distribution of `r` when applying the affine transform.

Raffaello Giulietti has updated the pull request incrementally with two additional commits since the last revision:

 - Added tests.
 - Align code comment with @implSpec.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12719/files
  - new: https://git.openjdk.org/jdk/pull/12719/files/bc0021cd..b867d275

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12719&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12719&range=06-07

  Stats: 356 lines in 2 files changed: 354 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12719.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/12719/head:pull/12719

PR: https://git.openjdk.org/jdk/pull/12719