RFR: 8348303: Remove repeated 'a' from ListSelectionEvent

[Alexey Ivanov]

A trivial change which removes repeated ‘a’ from the [javadoc for the `ListSelectionEvent` class](https://docs.oracle.com/en/java/javase/21/docs/api/java.desktop/javax/swing/event/ListSelectionEvent.html):

> “The change is limited to **a a** single inclusive interval.”

In addition to the above, I 
* expanded the wildcard imports,
* marked up `firstIndex` and `lastIndex` with `{@code}` in the class constructor parameter description (for consistency), and
* used a lower-case _“string”_¹ in the `@return` for `toString()` which aligns with the usage in [`Object.toString()`](https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/Object.html#toString()).

¹ The word _“string”_ refers not to the `String` class but rather to a string in its literal meaning.

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Commit messages:
 - Use lower-case “string” in @return for toString()
 - Mark up firstIndex and lastIndex with {@code}
 - 8348303: Remove repeated 'a' from ListSelectionEvent

Changes: https://git.openjdk.org/jdk/pull/23240/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23240&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348303
  Stats: 6 lines in 1 file changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/23240.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23240/head:pull/23240

PR: https://git.openjdk.org/jdk/pull/23240