[cfe] Include (super)-initializing-formal modifier in ast-to-text

This adds the initializer-formal and super-initializer-formal modifiers to the ast-to-text output.

These flags are used by backends, so we should expect when these are present.

Triggered by discussion on https://github.com/dart-lang/sdk/issues/62645

TEST=existing

Change-Id: I3eec128c912249bc907931bcf01b52c0ec1eda62
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/494080
Reviewed-by: Jens Johansen <jensj@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Johnni Winther <johnniwinther@google.com>

pkg/kernel/lib/text/ast_to_text.dart

@@ -2787,6 +2787,11 @@ class Printer extends VisitorDefault<void> with VisitorVoidMixin {
       writeModifier(node.isSynthesized && node.name != null, 'synthesized');
       writeModifier(node.isHoisted, 'hoisted');
       writeModifier(node.isWildcard, 'wildcard');
+      writeModifier(node.isInitializingFormal, 'initializing-formal');
+      writeModifier(
+        node.isSuperInitializingFormal,
+        'super-initializing-formal',
+      );
       writeModifier(node.isErroneouslyInitialized, 'erroneously-initialized');
       bool hasImplicitInitializer =
           node.initializer is NullLiteral ||