Generate scaffolding for an MLIR dialect

The idea is to create one place under experiments/ where all MLIR dialects live, and make an automated tool that can generate scaffolding for new dialects. The resulting dialect should be a self-contained C++ library that can be included in other projects.

Files to generate:

• CMakeLists.txt
• include/{path}/CMakeLists.txt (calls add_mlir_dialect)
• include/{path}/{dialect}Dialect.h
• include/{path}/{dialect}Dialect.td
• include/{path}/{dialect}Ops.h
• include/{path}/{dialect}Ops.td
• include/{path}/{dialect}Types.h
• include/{path}/{dialect}Types.td
• lib/{path}/CMakeLists.txt (calls add_mlir_dialect_library)
• lib/{path}/{dialect}Dialect.cpp
• lib/{path}/{dialect}Ops.cpp
• lib/{path}/{dialect}Types.cpp
• lib/{path}/opt/CMakeLists.txt
• lib/{path}/opt/main.cpp