time: implement the encoding.(Binary|Text)Appender for Time

"Time.Marshal(Binary|Text)" could also gain some performance
improvements. Here is the benchmark highlight:

                │     old      │                 new                 │
                │    sec/op    │   sec/op     vs base                │
MarshalText-8     104.00n ± 3%   67.27n ± 2%  -35.32% (p=0.000 n=10)
MarshalBinary-8    31.77n ± 2%   12.13n ± 1%  -61.82% (p=0.000 n=10)
geomean            57.48n        28.57n       -50.30%

                │    old     │                  new                   │
                │    B/op    │   B/op     vs base                     │
MarshalText-8     48.00 ± 0%   0.00 ± 0%  -100.00% (p=0.000 n=10)
MarshalBinary-8   16.00 ± 0%   0.00 ± 0%  -100.00% (p=0.000 n=10)

                │    old     │                   new                   │
                │ allocs/op  │ allocs/op   vs base                     │
MarshalText-8     1.000 ± 0%   0.000 ± 0%  -100.00% (p=0.000 n=10)
MarshalBinary-8   1.000 ± 0%   0.000 ± 0%  -100.00% (p=0.000 n=10)

For #62384

Change-Id: I320421878a341abf8d668fd57b27292cdfa61330
GitHub-Last-Rev: e04f8df9c277481f5678208d3f1f59643bf5e429
GitHub-Pull-Request: golang/go#68942
Reviewed-on: https://go-review.googlesource.com/c/go/+/606655


Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>