RFR: 8369312: Refactor Float.toHexString() to avoid use of regex

[Joe Darcy]

Simple refactoring to avoid use the regular expressions. Existing tests in

java/lang/Double/ToHexString.java

cover the float conversions too.

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Commit messages:
 - JDK-8369312: Refactor Float.toHexString() to avoid use of regex

Changes: https://git.openjdk.org/jdk/pull/27780/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27780&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369312
  Stats: 10 lines in 2 files changed: 4 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/27780.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27780/head:pull/27780

PR: https://git.openjdk.org/jdk/pull/27780