This patch re-factors the driver code in LLVM Flang (frontend + compiler) to use the MLIR style. For more context, please see: https://discourse.llvm.org/t/rfc-coding-style-in-the-driver/
Most changes here are rather self-explanatory. Accessors are renamed to be more consistent with the rest of LLVM (e.g. allSource --> getAllSources). Additionally, MLIR clang-tidy files are added in the affected directories.
[1] https://mlir.llvm.org/getting_started/DeveloperGuide/
Depends on D124669