Support for multi-catch-clauses in try-statements

[wadoon]

Intended Change

This PR implements a new transformer for the KeYJavaTransformationPipeline that desugars modern Java exception handling constructs into their equivalent basic forms:

MultiCatchReducer transforms multi-catch clauses into multiple single catch clauses (per JLS 14.20).

These transformations enable KeY to verify code using these Java 7+ features by reducing them to the core try/catch/finally constructs already supported by the verification infrastructure.

Technical Details

For a multi-catch:

try {
    body
} catch (ExceptionType1 | ExceptionType2 e) {
    handler
}

Produces:

try {
    body
} catch (ExceptionType1 e) {
    handler
} catch (ExceptionType2 e) {
    handler
}

Supports:

• Any number of exception types in union
• Mixed single and multi-catch in same try
• Preserves finally-blocks
• Marks exception parameters as final (as required by multi-catch semantics)

Type of pull request

• Refactoring (behavior should not change or only minimally change)
• There are changes to the Java code

Ensuring quality

• I made sure that introduced/changed code is well documented (Javadoc and inline comments).
• I added new test case(s) for new functionality.
  • MultiCatchReducerTest.java - Tests for 2-3 exception types, mixed catches, and finally blocks
• I have tested the feature as an example: key.ui/examples/Java/MultiCatch/

[unp1]

Thanks.
Remaining issues:

1. MultiCatchReducer is not added to the pipeline. It is defined under …/transformations/pipeline/ but not registered in KeYJavaPipeline.createDefault(...), so it never runs during loading

2. Two or more multi-catch clauses in the same try are handled incorrectly. rewrite(...) iterates a snapshot (originalClauses) but mutates the live catchClauses via remove(i) / add(j++, …); after the first multi-catch expands, the snapshot index no longer matches the live list. As a result one clause is silently dropped and an un-expanded UnionType is left behind (which then fails to load). Reproducer:

   public class T {
       void m() {}
       int f() {
           try { m(); }
           catch (IllegalArgumentException | NullPointerException e) { return 1; }
           catch (ArithmeticException | ArrayStoreException e)       { return 2; }
           return 0;
       }
   }

   With the reducer registered this fails to load with Unsupported element … UnionType on the leftover ArithmeticException | ArrayStoreException, and the transformer output shows a clause from the first multi-catch is dropped. A single multi-catch (even mixed with single-type catches) works. Fix: track the live insertion position instead of removing by the snapshot index (e.g. rebuild the clause list, or remove the specific node).

3. The bundled example does not load. key.ui/examples/Java/MultiCatch/MultiCatch.java uses java.sql.SQLException, which is not in KeY's default classpath (JavaRedux)

4. Nit: the Javadoc note about ordering catch clauses by subtype relationship doesn't apply to a multi-catch's own alternatives, they must be disjoint (JLS §14.20), so there's no "more specific first" among them.

[wadoon]

Thanks. Remaining issues:
addressed