add content-assist for `@Qualifier` annotation

[martinlippert]

Provide content-assist for the param value of @Qualifier annotations, according to https://docs.spring.io/spring-framework/reference/core/beans/annotation-config/autowired-qualifiers.html.

This means that values for @Qualifier annotations can be bean names (from the bean index) or other "random" values that are already being used with the @Qualifier throughout the project.

[martinlippert]

This requires enhancing the index with detailed information about annotations being used on bean definitions and injection points, so that the content-assist can use that information generate meaningful proposals.