time/tzdata: new package

Importing the time/tzdata package will embed a copy of the IANA
timezone database into the program. This will let the program work
correctly when the timezone database is not available on the system.
It will increase the size of the binary by about 800K.

You can also build a program with -tags timetzdata to embed the
timezone database in the program being built.

Fixes #21881
Fixes #38013
Fixes #38017

Change-Id: Iffddee72a8f46c95fee3bcde43c142d6899d9246
Reviewed-on: https://go-review.googlesource.com/c/go/+/224588


Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>