Make EditingNG to imply NGFragmentItem

This patch changes EditingNG runtime enabled feature to imply NGFragmentItem.
When we invoke content_shell with --enable-blink-features=EditingNG,
NGFragmentItem is also enabled.

Change-Id: I66ada34cd5a6c80d1d495dd2a9ea0627d3fd5b7e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2276127
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#785268}

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -931,7 +931,7 @@
       // provides a convenient way for testing legacy layout code path in blink
       // unit tests.
       name: "LayoutNG",
-      implied_by: ["LayoutNGFieldset", "LayoutNGGrid", "EditingNG", "BidiCaretAffinity", "LayoutNGTable"],
+      implied_by: ["LayoutNGFieldset", "LayoutNGGrid", "BidiCaretAffinity", "LayoutNGTable"],
       status: "stable",
     },
     {
@@ -951,7 +951,7 @@
     },
     {
       name: "LayoutNGFragmentItem",
-      implied_by: ["LayoutNGBlockFragmentation", "LayoutNGFragmentTraversal"],
+      implied_by: ["LayoutNGBlockFragmentation", "LayoutNGFragmentTraversal", "EditingNG"],
       status: "test",
     },
     {