[Bug] False positive errors when a type parameter shadows a nested type name

Environment:
- ECJ: `Eclipse Compiler for Java(TM) v20250526-2018, 3.42.0` (latest on Maven Central)
- javac: 21.0.2

## Description

ECJ reports a set of false positive errors on valid code that compiles and runs correctly under `javac`. The root cause appears to be a **type-parameter name shadowing** issue: when a type parameter (`Op`) has the same name as a nested type (`BinaryExpr.Op`) declared in the same hierarchy, ECJ resolves the type parameter's usages to the wrong symbol. This in turn breaks the switch-exhaustiveness analysis of an enum switch, producing three spurious diagnostics.

Renaming the type parameter (e.g. `Op` -> `O`) makes the errors disappear, which points at the type-parameter resolution rather than the switch analysis itself.

## Steps to Reproduce

1. Create the following `demo/App.java`:

```java
package demo;

interface BinaryExpr {
interface Op { }

Op getOperator();
}

abstract class AbstractBinaryExpr implements BinaryExpr {
private final Op op;

public AbstractBinaryExpr(Op op) { this.op = op; }

@Override
public Op getOperator() {
return op;
}
}

final class ArithExpr extends AbstractBinaryExpr {
enum Op implements BinaryExpr.Op {
ADD, SUB
}

public ArithExpr(Op op) { super(op); }
}

public class App {

public static void main(String[] args) {
var e = new ArithExpr(ArithExpr.Op.ADD);
System.out.println(toStr(e));
}

public static String toStr(ArithExpr e) {
return switch(e.getOperator()) {
case ADD -> "+";
case SUB -> "-";
};
}
}
```

2. Compile with ECJ (batch compiler):

```
java -jar ecj-3.42.0.jar -source 21 -target 21 -d out demo/App.java
```

3. Issue reproduced
```
1. ERROR in .../demo/App.java (at line 36)
return switch(e.getOperator()) {
^^^^^^^^^^^^^^^
A switch expression should have a default case

2. ERROR in .../demo/App.java (at line 37)
case ADD -> "+";
^^^
ADD cannot be resolved to a variable

3. ERROR in .../demo/App.java (at line 38)
case SUB -> "-";
^^^
SUB cannot be resolved to a variable
```

However, the code compiles cleanly with no errors, and it runs correctly (prints `+`):
```
$ javac -d out demo/App.java # no output, exit 0
$ java -cp out demo.App
+
```

Affected: https://github.com/redhat-developer/vscode-java/issues/3816