CacheArray is a neat trick that was introduced in 7.x to introduce backwards compatible partially loaded large cache arrays.
As discussed in, there is no need for that in 8.x for at least the new implementations, so let's make this implementation with interface that we can use elsewhere too.
The long term goal is probably to get rid of CacheArray completely but that doesn't need to happen here.
PASSED: [[SimpleTest]]: [MySQL] 58,244 pass(es).
FAILED: [[SimpleTest]]: [MySQL] Unable to apply patch cache-collector-1858616-18.patch. Unable to apply patch. See the log in the details link for more information.
PASSED: [[SimpleTest]]: [MySQL] 58,460 pass(es).