Add new method Concat

[jason-zhj]

Add a new method Concat similar to the one in lodash, it creates a concatenated slice which is independent of the original slice, unlike append. This comes in handy when you need to create multiple slices from one base slice

[samber]

I'm going to change the prototype to Concat[T any](collections ...[]T) []T.

When using append() for chaining multiple collections, you have to do something like that: append(append(append(append(...), ...), ...), ...). Such implementation might lead to multiple reallocation and copy.

If lo.Concat receives a list of collections, I think we can preallocate and concat everything much faster.

[ccoVeille]

My question might be stupid, but how does it differs from slices.Concat from standard lib ?

@samber

[samber]

Uh, didn't know it exists 😂

[ccoVeille]

I often find things in slices package that I was looking for years, and I'm like wow.

but you are not the only one, that's why I opened dominikh/go-tools#1552