Taint is stuck in exception variable declaration of a catch clause: `catch(Exception e)`

**Description of the issue**
Taint can not flow out of the caught exceptions in catch clauses.
E.g.
```java
try {
} catch(Exception e) {
System.out.println(e.getMessage());
}
```
Here taint will not flow to `e.getMessage()`.

```codeql
import java
import semmle.code.java.dataflow.TaintTracking

class T extends TaintTracking::Configuration {
T() { this = "T" }

override predicate isSource(DataFlow::Node source) {
exists(CatchClause c | c.getVariable() = source.asExpr())
}

override predicate isSink(DataFlow::Node sink) { any() }
}

from DataFlow::Node source, DataFlow::Node sink, T t
where t.hasFlow(source, sink)
select source, sink
```

Link to query:
https://lgtm.com/query/3909102737996232443/