RFR: 8337205: Typo in Stack vs Deque Method table in Deque specification

[Turkhan]

This PR fixes `java.util.Deque`'s specification to name `peekFirst()` as an equivalent to Stack's `peek()` method since both of them don't throw when a collection is empty. This is not the case with the current `getFirst()` method.

Please let me know if I have to fix something in the PR. Will appreciate your guidance since this is my first PR to JDK.

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Commit messages:
 - 8337205: Set Deque's peekFirst() method as equivalent to Stack's peek() method in the doc

Changes: https://git.openjdk.org/jdk/pull/20363/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20363&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337205
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20363.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20363/head:pull/20363

PR: https://git.openjdk.org/jdk/pull/20363