encoding: document that base32 and base64 do not use UTF-8
The invention of base32 and base64 predates the invention of UTF-8
and was never meant to output valid UTF-8.
By default, the output is always valid ASCII (and thus valid UTF-8)
except when the user specifies an alphabet or padding value
that is larger than '\x7f'. If that is done,
then the exact byte symbol is used rather than the UTF-8 encoding.
Fixes #60689
Change-Id: I4ec88d974ec0658ad1a578bbd65a809e27c73ea7
Reviewed-on: https://go-review.googlesource.com/c/go/+/505237
Run-TryBot: Joseph Tsai <joetsai@digital-static.net> Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>