Message Composer Extract union type

The message composer still generates incorrect typings for union arrays.

It should use something like:
```
CamelCasedProperties<
Extract<
ExecuteMsg,
{
propose_modules: unknown
}
>['propose_modules']
>
```

for the camelCased signatures.

Locate the message composer and inspect how it generates camelCased signatures for union arrays. Reproduce the incorrect typings described in the issue, then verify that the generated type uses Extract on ExecuteMsg for the propose_modules property and that the resulting signatures are correct.

Vom Indexierungsmodell aus dem Issue-Text verfasst.