dlopen-notes: make output stable regardless of order of inputs

[bluca]

When multiple files are passed to dlopen-notes --sonames the output depends on the order of inputs in case the same soname is used with different priorities across different binaries:

$ ./dlopen-notes.py --sonames systemd-sbsign systemd-repart libblkid.so.1 required
libcrypto.so.3 recommended
libcryptsetup.so.12 recommended
libfdisk.so.1 required
libmount.so.1 required

$ ./dlopen-notes.py --sonames systemd-repart systemd-sbsign libblkid.so.1 required
libcrypto.so.3 required
libcryptsetup.so.12 recommended
libfdisk.so.1 required
libmount.so.1 required

sbsign requires libcrypto, and repart recommends it, so the output changes between required and recommended depending on which is passed last.

Fix it so that the highest priority for any given soname is always returned, regardless of the number of input binaries.

[behrmann]

Looks reasonable to me, does what it says on the tin (current binaries from systemd main required): instead of eagerly throwing out priorities and having the last one win, because the dictionary is built at the end, build the whole mapping first and always update to the priority. It's a bit circumspect, because the dict gets built twice, as noted below, but it does the job.

[behrmann]

Yep, that's what I meant. A bit more involved, but only builds the dictionary once.