RFR: 8313348: Fix typo in JFormattedTextField: 'it self'

[Alexey Ivanov]

A trivial change: ‘it self’ → ‘itself’.

In addition to it, I added a comma after ‘Similarly’ where it starts a sentence.

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Commit messages:
 - 8313348: Fix typo in JFormattedTextField: 'it self'

Changes: https://git.openjdk.org/jdk/pull/15087/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15087&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313348
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/15087.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15087/head:pull/15087

PR: https://git.openjdk.org/jdk/pull/15087