feat: matugen detects flatpak installations of zenbrowser and vesktop

[porkloin]

Follow-on PR for #1234. This PR actually updates the matugen.go logic in appendConfig to take an additional argument checkFlatpaks which can be a list of known flatpak IDs. For the majority of applications defined elsewhere in matugen.go the arg is assigned to nil. I've added two flatpaks which I happen to know the IDs for as an initial test case: zen browser and vesktop.

I also added some tests to show that this shouldn't block on cases where a user has both flatpak and bin installs, etc.

Let me know if you'd like to see anything else here!

[bbedward]

This will short circuit and not check the flatpaks if the first binary check doesnt find it in the path.

Should proably be like this:

cmdExists := len(checkCmd) == 0 || utils.AnyCommandExists(checkCmd...)
flatpakExists := len(checkFlatpaks) == 0 || utils.AnyFlatpakExists(checkFlatpaks...)

if !cmdExists && !flatpakExists {
    return
}

Same for appendTerminalConfig (should also get the flatpak argument)

[porkloin]

Good catch! Just fixed in a new commit, but == 0 check won't quite work on nil so it's slightly different but same general idea.

[bbedward]

len(slice) in golang results in 0 when the slice is nil , in many operations in GO nil slices behavior like empty slices.

Albeit, in this context it doesnt matter since the "skip evaluation" conditions are explicitly setting nil

But the distinction is

len(slice) == 0 evaluates to true for nil and pointers to an empty slice (not nil but empty slice)

checkCmd == nil only evaluates to true for nil pointer, but not for an empty slice.