Move the `DwarfGenerator` modules into their own library.

[CarlosAlbertoEnciso]

The llvm/unittests/DebugInfo/DWARF/DwarfGenerator.cpp[h] can generate DWARF debug info for unit tests.

These components should be moved into their own library so they can be shared between unittests.
Currently they are used by the DWARF and llvm-debuginfo-analyzer unittests.

[llvmbot]

@llvm/issue-subscribers-debuginfo

Author: Carlos Alberto Enciso (CarlosAlbertoEnciso)

The `llvm/unittests/DebugInfo/DWARF/DwarfGenerator.cpp[h]` can generate DWARF debug info for unit tests.

These components should be moved into their own library so they can be shared between unittests.