Revert "Revert "Refactor OperationName to use virtual tables for dispatch (NFC)""

This streamlines the implementation and makes it so that the virtual
tables are in the binary instead of dynamically assembled during initialization.
The dynamic allocation size of op registration is also smaller with this
change.

This reverts commit 7bf1e441
and re-introduce e055aad5
after fixing the windows crash by making ParseAssemblyFn a
unique_function again

Differential Revision: https://reviews.llvm.org/D141492