Graphviz generator crashes on `sizeof<>` expressions

[jtbandes]

The following definition crashes the graphviz generator:

meta:
  id: asdf
  file-extension: asdf

seq:
  - id: x
    size: sizeof<xx>
    
types:
  xx:
    seq:
      - id: a
        type: u1

I believe the problem is that this match doesn't handle sizeofs.

This is preventing log/mcap.ksy from having a svg generated at https://formats.kaitai.io/mcap/