Print an error message when a package isn't found when using -Si

[jdholtz]

This fixes the second issue discussed in #2472. It uses the same solution to find missing packages as in #2717, so if both of these get merged, I can create a common function to not duplicate this logic.

A couple of notes on how yay -Si <pkg> differs from pacman -Si <pkg> (not huge deals IMO):

1. The exit code from yay is 1 when a package isn't found, whereas with pacman the exit code is the number of packages not found (mod 256)
2. pacman prints all packages in order of being specified, including errors. E.g specifying cmatrix, nonexistent, firefox will show the cmatrix info, then 'error: package 'nonexistent' not found, then firefox info. Yay will print all packages not found first, then repo packages, then AUR packages due to the way the implementation is structured.

Both of these are not big deals, but wanted to point them out in case. I did not update/add any tests as this is just for error printing, but can do so if that is desired.

[Jguer]

I'm ok with it but there's a bunch of users that run CI environments and want yay to ignore all types of errors in missing packages. I think since this doesn't change the missing logic, we should be ok.
Merging it in and we'll see based on feedback