[m-rev.] diff: make text_{in,out}put _stream standalone types

[Zoltan Somogyi]

Since we have agreement on the principle and the changes are trivial,
this does not need review.

Zoltan.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Log.stream1
Type: application/octet-stream
Size: 465 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20230424/697cbda8/attachment-0002.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: DIFF.stream1
Type: application/octet-stream
Size: 60403 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20230424/697cbda8/attachment-0003.obj>