RFR: 8339934: Simplify Math.scalb(double) method [v3]

[Raffaello Giulietti]

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

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

  Introduce primPowerOfTwoD and make use of it.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20948/files
  - new: https://git.openjdk.org/jdk/pull/20948/files/2b7c7061..1095824a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20948&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20948&range=01-02

  Stats: 15 lines in 1 file changed: 6 ins; 1 del; 8 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