RFR: 8093: Rules dependant on GarbageCollectionInfoRule throw NPE if there is no gcInfo

[Alex Macdonald]

This short PR addresses a bug where the four gc rules that depend on GarbageCollectionInfoRule will throw a NPE when evaluating in the case there is no GC information.

This (probably?) won't happen too often, as it requires the jdk.GarbageCollection event to be enabled but never recorded. I was interacting with a handful of short recordings when I ran into this. 
![event-browser](https://github.com/openjdk/jmc/assets/10425301/cac8ceaa-34b6-46b3-8a42-14af375a7c51)

The GarbageCollectionInfoRule has it's jdk.GarbageCollection EventAvailability set to AVAILABLE, which means it's looking for the event to be both enabled and have data before evaluating.

The four rules that depend on it have their EventAvailability set to ENABLED, so these rules will run if the event is enabled but even if there's no data. Because GarbageCollectionInfoRule never runs, the aggregate object in the dependant rules is null ([[example]](https://github.com/openjdk/jmc/blob/master/core/org.openjdk.jmc.flightrecorder.rules.jdk/src/main/java/org/openjdk/jmc/flightrecorder/rules/jdk/memory/HeapInspectionRule.java#L102) [0]), so a NPE is thrown when trying to evaluate it.

The fix here is to make these rules require the gc events to be available in order to proceed, similar to how GarbageCollectionInfoRule does.

Before:
![before](https://github.com/openjdk/jmc/assets/10425301/e4eb6b7f-4055-491c-a5b3-ded5608644d7)

After:
![after](https://github.com/openjdk/jmc/assets/10425301/3caf81ac-b8a8-4b8b-a87f-4bc11f14c8c2)

[0] https://github.com/openjdk/jmc/blob/master/core/org.openjdk.jmc.flightrecorder.rules.jdk/src/main/java/org/openjdk/jmc/flightrecorder/rules/jdk/memory/HeapInspectionRule.java#L102

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Commit messages:
 - 8093: Rules dependant on GarbageCollectionInfoRule throw NPE if there is no gcInfo

Changes: https://git.openjdk.org/jmc/pull/498/files
 Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=498&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8093
  Stats: 4 lines in 4 files changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jmc/pull/498.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/498/head:pull/498

PR: https://git.openjdk.org/jmc/pull/498