Add Constant Type and Operators

[MrBurmark]

Add a constant type that takes a compile-time value as a template parameter. Support arithmetic between constants that produces a constant.

Deprecate integral_constant in favor of constant.

constant<0> zero;
constant<1> one;
auto two = one + one;
static_assert(two == 2);
static_assert(std::same_as<decltype(two), constant<2>>);

The ultimate goal with this is use it as part of a RAJA::transparent_range class that I'm thinking about adding that stores the input begin, end, and stride exactly as they were given. My hope is to improve some cases in RAJAPerf and beyond where the BASE and RAJA differ by knowledge of such exact values. For example we often assume that ranges start at 0 but RAJA ranges always have a runtime begin value, knowledge of which does not cross the host device barrier. This is responsible for some differences between kernel which takes its ranges on the host and launch which takes ranges on the device.

[MrBurmark]

This overloads logical and and or so operations between constants remain constants. However this does break short-circuiting if both operands are constants. I'm not sure if this is a big deal or not since presumably constants are generated in constant expressions. Though of course could always return constant from a function with side-effects. So I'm not sure if I'm going to keep these overloads.

[MrBurmark]

@trws Are there additional concerns related to template instantiations in constant expressions and things like that that short-circuiting also has a bearing on?