Change DelegatedInkTrails to experimental

The delegated ink trail feature is now adding an ink trail to the
screen, so I'd like to make it experimental so its easier for myself
and web developers to test it and see how it works.

Bug: 1052145
Change-Id: I4cb6167c68cadb8f5b2d3f4c6b0e67507b50d53c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2503317Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Mario Bianucci <mabian@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#821741}

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -683,7 +683,7 @@
     },
     {
       name: "DelegatedInkTrails",
-      status: "test",
+      status: "experimental",
     },
     {
       name: "DesktopCaptureDisableLocalEchoControl",