Reworks the error message reporting that was just added to WVCryptoPlugin so
that it reports detailed error messages to the app (because the error codes
cannot be relied upon to reach the app intact) and so that it always reports
custom errors so that the detailed error message is passed to the app.
Bug: 8621516
Merge of https://widevine-internal-review.googlesource.com/#/c/5031/ from
widevine git to android git.
Change-Id: Id7a517fb6e4e772ffea4c779a8ee52b357345a08
c1474b9912