RFR: 8365832: Refactor FloatingDecimal [v2]

[Shaojin Wen]

> Since FloatToDecimal and DoubleToDecimal are used in Float.toString and Double.toString, some code in FloatingDecimal is not used. This refactoring is to remove the unused code and reuse DecimalDigits to reduce duplication of code.

Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:

  Update src/java.base/share/classes/java/text/DigitList.java
  
  Co-authored-by: Thomas Zimmermann <zimmi at users.noreply.github.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/23311/files
  - new: https://git.openjdk.org/jdk/pull/23311/files/df2d9e47..823ecb13

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23311&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23311&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/23311.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23311/head:pull/23311

PR: https://git.openjdk.org/jdk/pull/23311