More strict IndentationWidth

This addresses a problem I felt stood in the way of adding auto-correct support in `IndentationWidth`. Right now we can write
```ruby
x = if a
  b
end
```
or
```ruby
x = if a
      b
    end
```
without any complaint from `IndentationWidth`. We usually want to enforce one style at a time and make it configurable, rather than supporting two at the same time.

There are a few different ways we can solve this. I've chosen to hitch on to `EndAlignment` and its configuration.