Fix logging redirection bug with pager

Fix logging redirection bug with pager

I noticed yesterday that if gdb output is redirected to a file, the
pager will still be active.  This is irritating, because the output
isn't actually visible -- just the pager prompt.  Looking in bugzilla,
I found that this had been filed 17 years ago, as PR cli/8798.

This patch fixes the bug.  It changes the pagination code to query the
particular ui-file to see if paging is allowable.  The ui-file
implementations are changed so that only the stdout implementation and
a tee (where one sub-file is stdout) can page.

Regression tested on x86-64 Fedora 34.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=8798