FindPackageMessage: Remove extra whitespace from messages

This change addresses the mild annoyance of FindPackageHandleStandardArgs assembling the success message handed over to find_package_message() in such a way that if there is no version and/or component information available, then empty whitespaces show up at the end of the message printed to the console. This is particularly annoying in terminals or output windows configured to render whitespace characters, which is the default for eg. in VS Code's output window.

Topic-rename: FindPackageMessage-strip-spaces