Code cleanup: Change FormattersContainer::KeyType from SP to rvalue
There is now std::shared_ptr passed around which is expensive for manycore
CPUs. Most of the times (except for 3 cases) it is now just std::moved with no
CPU locks needed. It also makes it possible to sort the keys (which is now not
needed much after D66398).
Differential revision: https://reviews.llvm.org/D67049