Update OtlpMeterRegistryTest to run builds on Java 19

[izeye]

The following tests are failing:

• ofEmptyDoesNotAllocate() and andEmptyDoesNotAllocate() in TagsTest are failing as their allocated bytes have been changed from 0 to 16 somehow. I'm not sure what makes the difference, so it might be better to investigate further with a dedicated issue if possible.
• OtlpMeterRegistryTest.distributionSummaryWithHistogramBuckets() is failing as String representation for double has been changed slightly. See "Double.toString(double) and Float.toString(float) may Return Slightly Different Results" item in https://jdk.java.net/19/release-notes

For the first two tests, I just split the tests into two, one for prior versions and the other for 19+.

For the second test, I changed it to compare with double values, not with their String representation.

[shakuzen]

For the second test, I changed it to compare with double values, not with their String representation.

That sounds reasonable. I think we should add a comment in the code why we're doing that. Otherwise surely I (and probably others) will forget and it might get buried or not easily found in git history.
We should also check if this causes any issues in metrics backends ingesting from some applications on Java 19+ and some on earlier versions. Some buckets may end up slightly different. If it's a problem, maybe we need to do something different in main code.

[shakuzen]

I've opened #3436 for investigating the change in allocation.

[shakuzen]

I think we'll need these changes in the oldest applicable supported maintenance branch, since we will build those with JDK 19 also. That may require splitting the PR since OTLP was added in 1.9.x, but the Tags allocation tests were added to 1.8.x.

[sonatype-lift]

⚠️ 6 God Classes were detected by Lift in this project. Visit the Lift web console for more details.

[izeye]

@shakuzen Thanks for the feedback!

I extracted the TagsTest changes into #3437 for the 1.8.x branch and changed the base branch for this PR to the 1.9.x branch as you suggested.

[izeye]

For the record, I have seen the following error when I switched to the 1.9.x branch:

* What went wrong:
Could not open cp_settings generic class cache for settings file '/Users/user/IdeaProjects/micrometer/settings.gradle' (/Users/user/.gradle/caches/7.5.1/scripts/5qxrwyxrman55a9r3pyawbcqa).
> BUG! exception in phase 'semantic analysis' in source unit '_BuildScript_' Unsupported class file major version 63

It has been reproduced consistently, but after I switched to Java 17 and then back to Java 19, it's not reproducible anymore.

Based on gradle/gradle#20372, it seems that Gradle 7.6+ would support Java 19 officially.