RFR: 8336679: Add @implSpec for the default implementations in Process.waitFor() [v4]

[Naoto Sato]

> This is a simple doc-only change that follows up [JDK-8336479](https://bugs.openjdk.org/browse/JDK-8336479). A corresponding CSR has also been drafted.

Naoto Sato has updated the pull request incrementally with two additional commits since the last revision:

 - Update src/java.base/share/classes/java/lang/Process.java
   
   Co-authored-by: ExE Boss <3889017+ExE-Boss at users.noreply.github.com>
 - Update src/java.base/share/classes/java/lang/Process.java
   
   Co-authored-by: ExE Boss <3889017+ExE-Boss at users.noreply.github.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20285/files
  - new: https://git.openjdk.org/jdk/pull/20285/files/17c61d99..d3b3c800

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20285&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20285&range=02-03

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20285.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20285/head:pull/20285

PR: https://git.openjdk.org/jdk/pull/20285