Move cudf::char_utf8 definition from detail to public header

[davidwendt]

Description

Moves the cudf::char_utf8 definition from the cudf/strings/detail/utf8.hpp to cudf/types.hpp since it is declared in the public namespace and used in public functions.

Reference:

cudf/docs/cudf/source/conf.py

Lines 372 to 375 in 9acddc0

	# TODO: This type is currently defined in a detail header but it's in
	# the public namespace. However, it's used in the detail header, so it
	# needs to be put into a public header that can be shared.
	"char_utf8",

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[ttnghia]

@davidwendt Do we need to update cudf/docs/cudf/source/conf.py accordingly?

[davidwendt]

@davidwendt Do we need to update cudf/docs/cudf/source/conf.py accordingly?

That is a good question. I made @vyasr a reviewer. I think that I can just remove the comment.

[vyasr]

Thanks for this David! Yes, you can remove the comment as well as the line below it that actually says "char_utf8".

[vyasr]

/merge