RFR: 8129827: [TEST_BUG] Test java/awt/Robot/RobotWheelTest/RobotWheelTest.java fails

[Alexander Zvegintsev]

Test was written based on assumption that we will receive only one `mouseWheelMoved` event after `robot.mouseWheel(20)` call, but we can receive 20 intstead.

So the test is modified to accumulate wheel rotation values before checking.

Testing is green on all platforms.

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Commit messages:
 - initial

Changes: https://git.openjdk.java.net/jdk/pull/8305/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8305&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8129827
  Stats: 43 lines in 2 files changed: 32 ins; 6 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8305.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8305/head:pull/8305

PR: https://git.openjdk.java.net/jdk/pull/8305