[Core] Array and Dictionary set improvements

[AThousandShips]

• Make Dictionary.get_or_add check for read-only
• Add Dictionary.set for read-only enforcing assignments
• Add set_safe method to Array and Dictionary
• Add a range check to Array.set for safe usage and to match Vector

A number of different changes, largely related, can split them up if desired (the range check for Array.set could be cherry-picked if desired), and the set_safe isn't necessarily needed but added it just to see about the demand for it

Will look at adding some unit tests for read-only arrays to complement the dictionary ones

[Nazarwadim]

This check is unnecessary because it is checked in cowdata

[AThousandShips]

It is not, it crashes in Vector, because of the use of write:

godot/core/templates/vector.h

Lines 51 to 52 in fe01776

	_FORCE_INLINE_ T &operator[](typename CowData<T>::Size p_index) {
	CRASH_BAD_INDEX(p_index, ((Vector<T> *)(this))->_cowdata.size());

[Nazarwadim]

So going outside the array should crash. Especially if you added a set_safe() method.

[AThousandShips]

No, see the description for the reason and explanation :) It shouldn't like Vector, why have a separate set otherwise? It is the safe option over operator[]

The set_safe method might be better renamed, but the "safe" part isn't about it being safe, but that it can be used to check the details, originally named it set_check and might restore it to that to avoid confusion

Edit: Further, calling the setter on Variant doesn't crash in either case, so it isn't good to have it crash here either

[Nazarwadim]

Ah, then I think this can be added for get as well.

[AThousandShips]

Edit: My bad it does take that path, but the argument stands still, it returns a value so it can be expected to be valid, and this change is to match Vector, this also matches all other containers in the engine, like HashMap and VMap

It returns a const reference, which can't be safely done with a check