Make Canonicalizer modular

[WardBrian]

Currently, --print-canonical does a lot of different things to your code. Especially with the incoming deprecation changes, I think it would be great to have a way to pick and choose what it does.

I propose something like this, first discussed in #1042:

• All pretty printing is done with --auto-format.
• Add an additional argument which allows you to specify certain canonicalizations to use. For example, --auto-format --canonicalize=deprecations would only update deprecated features, not add/remove parenthesis etc. This is a comma separated list of options.
  By my count, we would have the following options to start:
  • deprecations - deprecated syntax and function replacement
  • includes - see Support pretty-printing without inlining #include-d code #1042
  • parenthesis - the current canonicalizer removes extra parenthesis
  • braces - the current canonicalizer adds {} around single-line if/else (...etc) blocks.
• We can then make --print-canonical a synonym for --auto-format --canonicalize=(all options enabled)

This also allows us in the future to add possible more opinionated canonicalizers which we don't want enabled for all users, or even mutually exclusive options.

I think this would be good to tackle alongside #24, and a similar design could be used for #549