RFR: 8294807: Fix typos and clarify javadoc for SunToolKit.realsSync

[Alexey Ivanov]

I fixed the typo “serie” → "series" which was highlighted by a spellchecker.

I also simplified the description, fixed the grammar, added `{@code}` around types, added link to `requestFocus` in the example.

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Commit messages:
 - Amend the javadoc for SunToolkit.realSync(long)

Changes: https://git.openjdk.org/jdk/pull/10563/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10563&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294807
  Stats: 16 lines in 1 file changed: 1 ins; 0 del; 15 mod
  Patch: https://git.openjdk.org/jdk/pull/10563.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10563/head:pull/10563

PR: https://git.openjdk.org/jdk/pull/10563