* Make trace testhelpers public
Move MockSpan and MockTracer out of internal package into the api/trace
directory.
* Do not move internal/trace/parent into testing dir
Leave internal/trace/parent/parent.go in the internal directory.
* Fix MockTracer Start method comments
Fix "TraceID".
* Run make precommit to cleanup go.mod
Cleanum go.mod and go.sum.
* Fix tracetest MockSpan structure alignment
Make MockSpan 80 bytes instead of 88 by fixing its alignment.
* Revert bridge/opentracing/internal/mock.go imports
Do not change imports lines in bridge/opentracing/internal/mock.go.