RFR: 8345403: Add more randomized tests to better cover FloatingDecimal parsing [v2]

[Raffaello Giulietti]

> `jdk.internal.math.FloatingDecimal` parsing is mostly exercised on inputs produced by `Float.toString` and `Double.toString`, but should be extended on more random inputs.

Raffaello Giulietti has updated the pull request incrementally with one additional commit since the last revision:

  Simplifications suggested by reviewers.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/22523/files
  - new: https://git.openjdk.org/jdk/pull/22523/files/64e21176..d719031f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22523&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22523&range=00-01

  Stats: 33 lines in 1 file changed: 11 ins; 17 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/22523.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22523/head:pull/22523

PR: https://git.openjdk.org/jdk/pull/22523