Fix snippets for dynamic arrays and maps

[xb-bx]

This PR fixes behavior of snippets for dynamic arrays and maps. Also added snippets for slices.

Current behavior:

arr := make([dynamic]int)
// becomes len(arr). it's fine
arr.len~ 

StructWithArray :: struct {
    arr_field: [dynamic]int
}
struc := StructWithArray {}
// becomes len(). should be len(struc.arr_field)
struc.arr_field.len~

return_array :: proc() -> [dynamic]int ---
// becomes len(). should be len(return_array())
return_array().len~ 

This PR fixes all of those cases and also adds snippets(len, for) for slices