blink: enable WebAuthenticationResidentKeyRequirement on stable

This ships support for the AuthenticatorSelectionCriteria.resident_key
(and its enum ResidentKeyRequirement type) and the corresponding
credProps extension in the Web Authentication API.

Intent to ship:
https://groups.google.com/a/chromium.org/g/blink-dev/c/_Lu3bV0JX-4/m/nl_EaDsBCQAJ

Bug: 1117630
Change-Id: I72f203e38bfbcf289016ec2884f10539eebbc646
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2618472Reviewed-by: Alex Russell <slightlyoff@chromium.org>
Commit-Queue: Martin Kreichgauer <martinkr@google.com>
Cr-Commit-Position: refs/heads/master@{#842723}

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -2117,7 +2117,7 @@
     },
     {
       name: "WebAuthenticationResidentKeyRequirement",
-      status: "experimental",
+      status: "stable",
     },
     // WebBluetooth is enabled by default on Android, ChromeOS and Mac.
     // It is also supported in Windows 10 which is handled in runtime_features.cc