Fix method-based injection

Currently, injection via methods is failing. Constructs like

```java
public void injectMe(@Ann MyType instance) { ... }
```

produces a `Key<Void>`, which is obviously wrong. For method-based injection to work, the code should look at the parameter of the method, not to the method itself.

This patch fixes this behavior, and correctly prepares a `Key<MyType>[annotations=@Ann]` for the above-mentioned snippet.