Revert "Remove SkTime from the public API"

This reverts commit a0572041af8e5317da14dd8fced3c72196545abb.

Reason for revert: causing Google3 breakage
https://fusion2.corp.google.com/triage/615500517562051498/10304141939179520/invocations/0e55b3cd-e449-411e-8c56-61adc92f6f0d/targets/%2F%2Fjavatests%2Fcom%2Fgoogle%2Fandroid%2Fwearable%2Ffitbit%2Fecg%2Fapi:EcgApiFitbitTest/log

Original change's description:
> Remove SkTime from the public API
>
> Change-Id: Ie310d9dad9f22bed5317568b9d862ec58dc3a66e
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/749817
> Reviewed-by: Herb Derby <herb@google.com>
> Commit-Queue: Kevin Lubick <kjlubick@google.com>

Change-Id: Ib267ad2b9bacc3cb3093f18912e8779f60bb11cd
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/752276
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Herb Derby <herb@google.com>
57 files changed