Add a slice append method

[jfecher]

Problem

We have a slice_push_back builtin but it'd also be helpful to have a append method to slices that loops over a slice and adds it to the end of another.

Happy Case

This does not need to be builtin:

fn append(mut self, other: Self) -> Self {
    for elem in other {
        self = self.push_back(elem);
    }
    self
}

Alternatives Considered

No response

Additional Context

No response

Would you like to submit a PR for this Issue?

No

Support Needs

No response