Revert "Move SkMSec out of public API"

This reverts commit 06cd203d0607e1c7b3e25d9f08eb2c67c11c268c.

Reason for revert: breaking Android roll (HWUI and a vendor fork currently rely on SkMSec)

Original change's description:
> Move SkMSec out of public API
>
> This seems a bit odd to be part of the API. It is unused by everything
> else in our public API, with the exception of SkParse::FindMSec which
> was both unused (by us and clients) and untested.
>
> Change-Id: Ib88e3c548a7f31f4fb59b05e99f907b34d7ff961
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/897150
> Reviewed-by: Brian Osman <brianosman@google.com>
> Commit-Queue: Kaylee Lubick <kjlubick@google.com>
> Auto-Submit: Kaylee Lubick <kjlubick@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>

Change-Id: I1a9530bc826919873708752bd80b01a63a6a2458
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/897716
Reviewed-by: Brian Osman <brianosman@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Kaylee Lubick <kjlubick@google.com>
Commit-Queue: Nolan Scobie <nscobie@google.com>
12 files changed