<Swing Dev> RFR: 8268087: Update documentation of the JPasswordField

[Sergey Bylokhov]

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Commit messages:
 - Update JPasswordField.java
 - Update JPasswordField.java

Changes: https://git.openjdk.java.net/jdk/pull/4296/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4296&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268087
  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4296.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4296/head:pull/4296

PR: https://git.openjdk.java.net/jdk/pull/4296