(dev/core#174) Add various utilities to support PSR-16

[totten]

Overview

This is an auxiliary PR in support of #12360. It reproduces the general utilities that help with a PSR-16 compliant cache provider.

After

• There are concrete-classes to represent cache exceptions.
• There is a base-class for end-to-end testing of caches.
• NaiveMultipleTrait handles bad inputs more correctly.
• CRM_Utils_Date has functions for calculating TTL and/or expiration based on NULL|int|DateInterval.

[civibot]

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[eileenmcnaughton]

I'm pretty comfortable the failed tests all relate to time-specific recurrent issues.

Merging this as it is helper functions / additional code. I agree in principle with the rationale for adding them