brp-mangle-shebangs: also mangle shebangs of JavaScript executables
    
    Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1998924
    
    Unfortunately, the MIME type of JavaScript executables is not text/... but
    application/javascript. See RFC 4329.
    
    After considering various approaches to fix this problem, including:
    
     1) limiting the number of characters `file` reads
     2) using `eu-elfclassify` instead of `file`
    
    This seems like the most sensible approach to fix this one particular problem.
    If more instances are found problematic in the future, we'll keep adding the
    MIME types.
    
    See the linked bugzilla, the eu-elfclassify pull request [1],
    and the devel mailing list thread [2] for details about this problem and
    the considered solutions.
    
    [1]: https://src.fedoraproject.org/rpms/redhat-rpm-config/pull-request/145
    [2]: https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/K3QCBUXYR6ZA34I777X6F2RYJKKECJLM/