time: support fractional timezone minutes in MarshalBinary

If the time is in 'LMT' and has fractional minute, then
`MarshalBinary()` and `UnmarshalBinary()` will encode/decode the time
in `timeBinaryVersionV2` in which the fractional minute is at
bit 15 and 16, and presented in seconds.

Fixes #39616

Change-Id: Ib762fb5fa26f54b1a8377a5dde0b994dd5a1236a
GitHub-Last-Rev: 455d7a2496ba67d4a82890b14d57000e1a8a1415
GitHub-Pull-Request: golang/go#40293
Reviewed-on: https://go-review.googlesource.com/c/go/+/243402


Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Carlos Amedee <carlos@golang.org>