Implement the encoding.(Binary|Text)Appender interfaces for "x509.OID".

Implement the encoding.BinaryAppender interface for "rand/v2.PCG" and "rand/v2.ChaCha8".

"rand/v2.ChaCha8.MarshalBinary" alse gains some performance benefits:

                           │     old      │                 new                 │
                           │    sec/op    │   sec/op     vs base                │
ChaCha8MarshalBinary-8       33.730n ± 2%   9.786n ± 1%  -70.99% (p=0.000 n=10)
ChaCha8MarshalBinaryRead-8    99.86n ± 1%   17.79n ± 0%  -82.18% (p=0.000 n=10)
geomean                       58.04n        13.19n       -77.27%

                           │    old     │                  new                   │
                           │    B/op    │   B/op     vs base                     │
ChaCha8MarshalBinary-8       48.00 ± 0%   0.00 ± 0%  -100.00% (p=0.000 n=10)
ChaCha8MarshalBinaryRead-8   83.00 ± 0%   0.00 ± 0%  -100.00% (p=0.000 n=10)

                           │    old     │                   new                   │
                           │ allocs/op  │ allocs/op   vs base                     │
ChaCha8MarshalBinary-8       1.000 ± 0%   0.000 ± 0%  -100.00% (p=0.000 n=10)
ChaCha8MarshalBinaryRead-8   2.000 ± 0%   0.000 ± 0%  -100.00% (p=0.000 n=10)

For #62384

Change-Id: I604bde6dad90a916012909c7260f4bb06dcf5c0a
GitHub-Last-Rev: 78abf9c5dfb74838985637798bcd5cb957541d20
GitHub-Pull-Request: golang/go#68987
Reviewed-on: https://go-review.googlesource.com/c/go/+/607079


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