Support interactive generation of operations.

[xlauko]

This should generate skeleton taking into account:

• dialect name
• operation name
• optional traits?
  • it might be nifty to provide checkbox list of most common traits/attributes
• arguments
• results
• regions
• whether generate builders
• assembly format?

Script appends new operation to Dialect/DialectOps.td file

[xlauko]

user should be able to omit unnecessary parameters