xbps-query -o is very slow

[paper42]

xbps stores the file list in plist files separate for each package. This means that xbps-query -o has to go through and parse many plist files before it finds the entries it's looking for. One sorted csv file listing all files tracked by xbps and their package names would speed this up a lot which would open many interesting possibilities in xbps-src like being able to detect dependencies of -devel packages with pkg-config files or moving shlibs from a common list in common/shlibs to individual packages.