`apt-cache` is just so incredibly slow that filtering against the final results
just doesn't cut it. Attempting to match against 'ac.*' (already taking
advantage of changing short search terms into prefix-only matches) would take
35 seconds, all of bottlenecked before the filtering step. This change uses more
of a heuristic to filter `apt-cache` results directly (before additional
filtering) to speed things up.
A variety of different limits from 100 to 5000 were timed and their result sets
compared to see what ended up artificially limiting valid completions vs what
took too long to be considered functional/usable and this is where we ended up.
GNU tr is not Unicode-aware, and was corrupting descriptions that had
non-ASCII characters.
Additionally, rather than using the Unicode private use characters, use
the ASCII/UTF-8 record separator character as it was intended.
The sed command could probably be rewritten to do all the heavy lifting
here, but would be even less readable.
Closes#8575.
Of note: The rpm/yum thing seems to be coupled, so I put it into one
function that tries the yum helper and uses the rpm path otherwise.
Zypper is already its own thing, so this should only be used for yum
and probably dnf (does that still have the helper?)
Zypper can be dropped, as that already used a separate function in the file.
Apk can just be inlined - it's literally one line for installed and another for all packages.
This function doesn't make any sense.
Most things that expect package names expect package names for *one
specific package manager*.
It only happens to work, most of the time, because most people only
have one package manager installed.
