diag: introduce diag_set_detailed()

diag_set() uses the current file and line as built-in macros.
In the future patches there are going to appear a couple of new
diag_set-like helpers which also would want to preserve the
original file and line.

For that they must be macros at least partially, like diag_set(),
and pass their own file and line. Because they are going not to be
very trivial and won't be implemented in the header.

The patch introduces diag_set_detailed() which allows to pass
custom file and line.

Needed for #6027