Ensure that initializers are only printed once in a PrintAst run

Otherwise the output becomes a DAG not a tree. Java achieves the same by omitting all PrintAst of `<obinit>` routines.

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

@@ -244,6 +244,21 @@ class ExprStmtNode extends ElementNode {
   }
 }
 
+/**
+ * A node representing a `KtInitializerAssignExpr`.
+ */
+class KtInitializerNode extends ExprStmtNode {
+  KtInitializerNode() { element instanceof KtInitializerAssignExpr }
+
+  override PrintAstNode getChild(int childIndex) {
+    // Remove the RHS of the initializer, because otherwise
+    // it appears as both the initializer's child and the
+    // initialize of the related field, producing a DAG not
+    // a tree and consequently unreadable output.
+    result = super.getChild(childIndex) and childIndex = 0
+  }
+}
+
 /**
  * Holds if the given expression is part of an annotation.
  */

java/ql/test/kotlin/library-tests/generics/PrintAst.expected

@@ -86,9 +86,8 @@ generics.kt:
 #   13|         0: [SuperConstructorInvocationStmt] super(...)
 #   13|         1: [BlockStmt] { ... }
 #   13|           0: [ExprStmt] <Expr>;
-#   13|             0: [AssignExpr] ...=...
+#   13|             0: [KtInitializerAssignExpr] ...=...
 #   13|               0: [VarAccess] t
-#   13|               1: [VarAccess] t
 #   13|     2: [Method] getT
 #   13|       5: [BlockStmt] { ... }
 #   13|         0: [ReturnStmt] return ...
@@ -96,6 +95,7 @@ generics.kt:
 #   13|             -1: [ThisAccess] this
 #   13|     2: [FieldDeclaration] T t;
 #   13|       -1: [TypeAccess] T
+#   13|       0: [VarAccess] t
 #   14|     4: [Method] f1
 #-----|       4: (Parameters)
 #   14|         0: [Parameter] t