RFR: 8304947: Unnecessary Vector usage in java.awt.MenuBar.shortcuts

[Andrey Turbanov]

Method `'java.awt.MenuBar#shortcuts` creates a 'Vector<MenuShortcut>', fills it and then returns its 'Enumeration elements()' as return value.
Instead of usage of legacy synchronized Vector here we can use ArrayList instead. Wrap it in Collections.enumeration to adapt to 'Enumeration' result type.

-------------

Commit messages:
 - [PATCH] Unnecessary Vector usage in java.awt.MenuBar.shortcuts

Changes: https://git.openjdk.org/jdk/pull/13149/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13149&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304947
  Stats: 13 lines in 2 files changed: 3 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/13149.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13149/head:pull/13149

PR: https://git.openjdk.org/jdk/pull/13149