RFR: 6674: Optimize finding of first start time and first & last end times

[Henrik Dafgård]

This optimization relies on the fact that event lanes are sorted by timestamp. This allows us to skip performing very costly comparisons when finding the first start time or first/last end times of an IItemCollection and instead just get the first or last events in each lane and find the event in that set that was earliest or last, respectively.

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Commits:
 - f6af24e4: Update RulesToolkit.java
 - 56a760ef: Optimize sliding window and other start time aggregations

Changes: https://git.openjdk.java.net/jmc/pull/31/files
 Webrev: https://webrevs.openjdk.java.net/jmc/31/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6674
  Stats: 123 lines in 10 files changed: 93 ins; 9 del; 21 mod
  Patch: https://git.openjdk.java.net/jmc/pull/31.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/31/head:pull/31

PR: https://git.openjdk.java.net/jmc/pull/31