Add a pass that builds a debug info scope for LLVMFuncOp (adding a DISubprogramAttr)

This may be seen as a hack, but it allows for any piece of MLIR to be able
to end up with DWARF debug info through LLVM.
Assuming the operations in the function have location such as FileLineCol,
this provides backtraces with line tables and allows to step in a debugger.
That makes this pass a perfect companion to -snapshot-op-locations

It was also the default behavior of MLIR to LLVM IR translation until MLIR
got support for proper debug info attributes.

Differential Revision: https://reviews.llvm.org/D144069