A new switch case for converting the source string type into a
destination RawBytes type avoids the reflection based conversion.
Speed up from old ~61.7ns/op down to ~49ns/op.

A second new switch case allows to convert and assign a source time.Time
type into a destination sql.RawBytes type. This switch case appends
the time to the reset RawBytes slice. This allows the reuse of RawBytes
and avoids allocations.

Fixes #20746

Change-Id: Ib0563fd5c5c7cb6d9d0acaa1d9aa7b2927f1329c
Reviewed-on: https://go-review.googlesource.com/66830
Run-TryBot: Daniel Theophanes <kardianos@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>