Make targets an api exposed via wac-types

[fibonacci1729]

Closes #159

Example output:

error: Imports present in the component but not in the target world:
  - wasi:cli/environment@0.2.3
  - wasi:cli/exit@0.2.3
  - wasi:cli/stderr@0.2.3
  - wasi:cli/stdin@0.2.3
  - wasi:cli/stdout@0.2.3
  - wasi:cli/terminal-input@0.2.3
  - wasi:cli/terminal-output@0.2.3
  - wasi:cli/terminal-stderr@0.2.3
  - wasi:cli/terminal-stdin@0.2.3
  - wasi:cli/terminal-stdout@0.2.3
  - wasi:clocks/wall-clock@0.2.3
  - wasi:filesystem/preopens@0.2.3
  - wasi:filesystem/types@0.2.3
  - wasi:io/error@0.2.3
  - wasi:io/streams@0.2.3
Exports required by target world but not present in the component:
  - wasi:http/incoming-handler@0.2.0: Instance(InterfaceId(Id { idx: 88 }))