This adds a method to CodeWriter which allow for writing without
having a trailing newline or leading indentation inserted. This can
be very useful when you want to write part of a line without knowing
what the whole line will contain.

This does preserve some safety in that it will intercept newlines to
treat them as normal, but it is still potentially dangerous if not
used carefully.

This adds support for serializing a Smithy model into the IDL format.

Shapes can be filtered case-insensitively because they are required
to be case-insensitively unique. Metadata doesn't have that same
constraint though, so filtering them as such would lead to a non-
deterministic ordering.

This simplifies various bits of the internals, for instance by
discarding much manual tinkering of sorting.

This updates the `compareTo` on shapeIds to be case-insensitve by
default, with a case-sensitive tie-breaker. Though technically that
means we could be comparing a given shape twice, practically the
likelihood is low since ShapeId's in a model must be
case-insensitively unique.