Implement "defaulted" instantiation arguments

If a component being instantiated with a new expression has a `unlocked-dep` or `locked-dep` import and the import has not been satisfied by an argument to the new expression, `wac` should implicitly resolve and instantiate a (shared) instance of the dependency and project into its exports, passing the result as the argument.

Example:

Package `foo:bar`:

```wat
(component
// ...
(export "f" (func 0))
)
```

Package `bar:baz`:

```wat
(component
(import "unlocked-dep==0.1.0}>" (func))
)
```

Composition:

```wac
let i = new bar:baz { };
```

Then `foo:bar@0.1.0` should get resolved and instantiated, `f` should be aliased from the export, and the alias passed in as the argument for `unlocked-dep=`.

The instantiated dependency would either have all of its imports satisfied by implicit imports or by recursively instantiated dependencies for any `unlocked-dep` and `locked-dep` imports.

It would be an error if the (transitive) dependencies fail to resolve.