Transform class references in connect-migrate

[timostamm]

This updates the connect-migrate command to replace imports for a message class with a schema import, and update:

• "new" expressions to a create() call
• calls to the static methods fromBinary, fromJson, fromJsonString
• isMessage calls

When the identifier is used elsewhere, add a type import for the message type.
When the message is a well-known type, update to import from @bufbuild/protobuf/wkt.

Before we can merge this, we should:

• not add type imports in .js files
• handle import as
• handle require calls