While looping here does work fine, it's mildly inefficient, particularly
if the number of members being added is large, because it can result in
multiple allocations over the period of the insertion, depending on how
much extra memory push_back may allocate for successive elements.
Instead, we can just tell the std::vector that we want to slap the whole
contained sequence at the back of it with insert, which lets it allocate
the whole memory block in one attempt.
By taking the std::string by value in the constructor, this allows for
certain situations where copies can be elided entirely (when moving an
instance into the constructor)
e.g.
std::string var = ...
...
... = LiteralString(std::move(var)) // Or whatever other initialization
// is done.
No copy will be done in this case, the move transfers it into the
constructor, and then the move within the initializer list transfers it
into the member variable.
tl;dr: This allows the calling code to potentially construct less
std::string instances by allowing moving into the parameters themselves.
