Document behavior of modulo operator

[qwertystop]

Different languages and contexts have different default behaviors for modulo where one or both operands are negative. "The remainder of an integer division" is underspecified. As such, clarification is in order.

[dalexeev]

It would be great to use a description consistent with the GDScript modulo operator. Expression supports utility functions too.

godot-docs/tutorials/scripting/gdscript/gdscript_basics.rst

Lines 330 to 331 in 183d0e3

	3. For negative values, the ``%`` operator and ``fmod()`` use `truncation <https://en.wikipedia.org/wiki/Truncation>`_ instead of rounding towards negative infinity.
	This means that the remainder has a sign. If you need the remainder in a mathematical sense, use the :ref:`posmod() <class_@GlobalScope_method_posmod>` and

[qwertystop]

That this page uses "modulo" and the other (linked by @dalexeev ) uses "remainder" led to me only finding this and not the other when I searched – terminology around this is often a bit fuzzy. Even if one is more technically accurate than the other, it might be useful to have both in docs to make sure it is relatively searchable.