QDoc: Add source locations to reports

QDoc has several ways to provide feedback to users during a run by
printing messages to the output. One of those is the "report", which
isn't considered a warning and thus doesn't contribute to the warning
count of a documentation build. These reports omit source
locations. This makes reported problems, such as images without alt
text, difficult to locate. Also, because of how `Location::report()` is
implemented, identical reports from different locations appear only
once, which leaves other occurrences hidden. This differs from how QDoc
issues its warnings, and makes the report less helpful for users trying
to improe their documentation set based on QDoc's findings.

This change makes it so that reports include filenames and line numbers.
This aids authors and automated tools in locating reported
problems. Reports from from distinct locations are preserved, while
duplicates at the same location are suppressed. Reports remain
informational and do not affect build success.

[ChangeLog][QDoc] Reports include source locations when available.
Identical reports from different source locations appear separately.

Fixes: QTBUG-150987
Change-Id: I712a4bcb5ce0e666ba04abaa327f10b44779847b
Reviewed-by: David Boddie <david.boddie@qt.io>
Reviewed-by: Jerome Pasion <jerome.pasion@qt.io>