Slider NG: Enable it by default

After this CL, <input type=range> uses LayoutNG.

Bug: 1040826
Change-Id: I8e02b38c3b58266ee3f9298e81c9a6a5acbd9749
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2444631Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813111}

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -1006,7 +1006,7 @@
     {
       name: "LayoutNGForControls",
       depends_on: ["LayoutNG"],
-      status: "experimental",
+      status: "stable",
     },
     {
       name: "LayoutNGFragmentItem",