RFR: 8368968: FloatingDecimal: Clean up unused code [v2]

[Johannes Graham]

> This is a followup to https://github.com/openjdk/jdk/pull/27118, to clean up resulting unused code.
> - remove `getChars`, `isExceptional` and `isNegative` 
> - remove `ExceptionalBinaryToASCIIBuffer`; throws `IllegalArgumentException` instead of returning an instance of that.(Caller already asserts non-exceptional arg)

Johannes Graham has updated the pull request incrementally with one additional commit since the last revision:

  Update src/java.base/share/classes/jdk/internal/math/FloatingDecimal.java
  
  Co-authored-by: Raffaello Giulietti <raffaello.giulietti at oracle.com>

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/27581/files
  - new: https://git.openjdk.org/jdk/pull/27581/files/8531f73b..d7d4938e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27581&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27581&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27581.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27581/head:pull/27581

PR: https://git.openjdk.org/jdk/pull/27581