RFR: 8339934: Simplify Math.scalb(double) method

[Raffaello Giulietti]

`Math.scalb(double)` can be simplified, removing a loop and using larger/smaller factors.

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Commit messages:
 - 8339934: Simplify Math.scalb(double) method

Changes: https://git.openjdk.org/jdk/pull/20948/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20948&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339934
  Stats: 57 lines in 1 file changed: 6 ins; 35 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/20948.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20948/head:pull/20948

PR: https://git.openjdk.org/jdk/pull/20948