Introduce and use SwitchBlock instead of StmtParent for switch-statement-or-expression

java/ql/lib/semmle/code/java/Statement.qll

@@ -428,6 +428,13 @@ class SwitchStmt extends Stmt, @switchstmt {
   override string getAPrimaryQlClass() { result = "SwitchStmt" }
 }
 
+/**
+ * A `switch` statement or expression.
+ */
+class SwitchBlock extends StmtParent {
+  SwitchBlock() { this instanceof SwitchStmt or this instanceof SwitchExpr }
+}
+
 /**
  * A case of a `switch` statement or expression.
  *