Optimizations for trivial types

[hpvb]

Relying on various compiler primitives we can reduce the work done
in our memory allocators and CowData. For types with trivial ctors or
dtors we can skip looping over all elements when creating, resizing,
and destroying lists of objects.

These primitives are supported by clang, msvc, and GCC. However, once
we've moved to C++11 we can rely on several std:: primitives that do
the same thing and are standardized.

In my testing the extra conditionals introduced here get removed from
the generated program entirely as the results for these primitives is
known at compile time.

[hpvb]

I've removed the 'fixes' relation to the issue as @Zylann doesn't really feel this completely addresses his concerns. However these are some of his benchmarking results so I still think this should go in:

@hpvb here are the times I get from the same benchmark:

Debug, without your PR:

Re-using the vector: 515ms
Not re-using the vector: 539ms

Debug, with your PR:

Re-using the vector: 39ms
Not re-using the vector: 65ms

Release-tools, without your PR:

Re-using the vector: 225ms
Not re-using the vector: 336ms

Release-tools, with your PR:

Re-using the vector: 39ms
Not re-using the vector: 63ms

Note: there seem to be a bit of random at stake, because some rare times, for the same test, the total durations I recorded were up to 3 times less or more, so I wrote down the most occurring times.

[akien-mga]

Thanks!

[akien-mga]

Now that Godot 3.1 has been released, we don't plan to cherry-pick new features and enhancements to the 3.0 branch, unless there is very strong support in favor of it. Removing cherrypick label for 3.0.