[MLIR][DLTI] Add mangling style (#125875)
Add mangling style as a spec entry to datalayout, and implemented
importing and exporting LLVM IR to MLIR (LLVM dialect).
Its represented as string as the scope of this PR is to preserve info
from LLVM IR, so client in MLIR still need to map deduce the meaning of
the string, like "e" means ELF, "o" for Mach-O, etc.
it addresses one of issues mentioned in this
[issue](https://github.com/llvm/llvm-project/issues/126046)
