Even though optional, it'll be better than the OS name when showing it
as an origin, because it reflects who created it, not what the OS is.

This does two things:
a) is stores only non-empty strings;
b) when a variable is duplicated in the file, free the previous value
   first, to avoid a memory leak.

The vendor name means whom created it, while the (OS) name is a name
of the operating system. The way GsApp uses this string means
the vendor name is more accurate. As it's optional, fallback
to the OS name when not set.

Backport !2028 “Prefer vendor name from os release in app origin” to gnome-46

See merge request GNOME/gnome-software!2033

Resolves: #2519

Backport !2054 “packagekit: Add support for the new action-state info enums” to gnome-46

See merge request GNOME/gnome-software!2056

The extras page can show various app kinds, while the "Install All"
button was meant to be shown only for codecs, thus limit when it's
visible.

Closes https://gitlab.gnome.org/GNOME/gnome-software/-/issues/2603

Backport !2067 “gs-extras-page: Let install in bulk only codecs” to gnome-46

See merge request GNOME/gnome-software!2068