sshd/terminal: Upstream changes to golang.org/x/term

[shazow]

We have some important changes in our local fork of golang.org/x/term (formerly x/crypto/terminal), need to upstream them.

• Primarily 8c7ea17 via sshd/terminal: Add fullwidth check for CJK in visualLength #339

[abitrolly]

@shazow so where to put this commit? Seems to relate to getSize call. However, I am not sure why getSize is not sufficient?

https://cs.opensource.google/go/x/term/+/refs/tags/v0.25.0:term_unix.go;l=59-65

[shazow]

@abitrolly getSize returns the size of the window. We need the width of a character/string. The commit includes a test that needs to pass, so could run it to see if it has been fixed upstream. I haven't checked.