RFR: 8300038: Make new version of JNU_GetStringPlatformChars which checks for null characters [v2]

[Michael McMahon]

> This PR creates a new version of the JNI utility function JNU_GetStringPlatformChars called JNU_GetStringPlatformCharsStrict, which performs additional validation of the returned string, namely that it does not contain any embedded NULL characters. If any such characters are found the function returns NULL with an IAE pending. The change also switches usage in the networking native code to use the new function.
> 
> This cautious approach was taken rather than changing the behavior of the existing function as each native code area needs to review the effect of making the switch. Otherwise, surprising behavior changes might occur (eg undocumented IAE being thrown to user code instead of some other exception).

Michael McMahon has updated the pull request incrementally with one additional commit since the last revision:

  test comment update

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14083/files
  - new: https://git.openjdk.org/jdk/pull/14083/files/8cf24635..0acc456a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14083&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14083&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14083.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14083/head:pull/14083

PR: https://git.openjdk.org/jdk/pull/14083