RFR: 8316187: Modernize an example in StringTokenizer

[Pavel Rappo]

This modernizes an example to use the extended for-statement introduced in JDK 1.5.

I understand that StringTokenizer is a legacy class. But legacy or not, a class shouldn't promote older constructs when newer fit better. Especially when advising on preferred alternatives to itself.

That said, I wouldn't go as far as to use `var` anywhere in that example: JDK 10, which introduced `var`, might still be relatively new to some. Nor would I inline the call to `String.split` in the for-statement to dispense with the `String[] result` variable: I reckon it's good for a reader unfamiliar with `String.split` to see the type it returns.

Perhaps one additional thing to ponder is this: we could either add `@see` to point to `String.split` or make the whole example a `@snippet`, which `@link`s code to the definition of `String.split`.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/15716/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15716&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316187
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15716.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15716/head:pull/15716

PR: https://git.openjdk.org/jdk/pull/15716