RFR: 8343453: Modernize FloatingDecimal tests [v2]

[Raffaello Giulietti]

> Simplify tests.

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

  Remove test jdk/jdk/internal/math/ToString.java as well.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/21840/files
  - new: https://git.openjdk.org/jdk/pull/21840/files/53496174..e1f8b895

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21840&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21840&range=00-01

  Stats: 73 lines in 1 file changed: 0 ins; 73 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/21840.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21840/head:pull/21840

PR: https://git.openjdk.org/jdk/pull/21840