[WIP] Enhancements to Operators and Reduction Scaffolding

[willkill07]

Summary

• This PR is an enhancement with some bug fixes and new features

It does the following:

• Introduce BitXor reduction
• operators::largest didn't have the correct overload for integral GPU types
• op_adapter template simplified
• static_assert checks introduced for:
  • integral types for bitwise operations
  • associative operators for reductions

To Do

• testing
• continue to evaluate current operator and reduction mechanisms

[codecov]

Codecov Report

Merging #868 into develop will decrease coverage by 0.041%.
The diff coverage is 100.000%.

@@              Coverage Diff              @@
##           develop      #868       +/-   ##
=============================================
- Coverage   96.829%   96.788%   -0.042%     
=============================================
  Files           99        99               
  Lines         2555      2553        -2     
=============================================
- Hits          2474      2471        -3     
- Misses          81        82        +1     

Impacted Files	Coverage Δ
include/RAJA/pattern/detail/reduce.hpp	100.000% <100.000%> (ø)
include/RAJA/util/Operators.hpp	100.000% <100.000%> (ø)
include/RAJA/policy/atomic_builtin.hpp	98.076% <0.000%> (-1.924%)	⬇️
include/RAJA/util/sort.hpp	95.402% <0.000%> (-0.053%)	⬇️

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