Support multiple locations per Report

Relates to reports filtering - https://github.com/orgs/dotnet/projects/373/views/1?pane=issue&itemId=54234918

https://github.com/dotnet/msbuild/pull/9735#discussion_r1496544037

Some reports will relate to multiple paths - make it possible to specify them, while specifying whether one is main or all are equal (in which case equal report should be present to user regardless of the order of paths specified when constructing - so that nondetermionistic order of execution doesn't lead to nondeterministic results)