[css-text] Ship the 'line-break: anywhere' feature

This CL changes the runtime flag to stable and enables the feature by
default.

The intent-to-ship request [1] has been approved, under the condition of
improving the test suite and increasing the testing coverage of the
feature. These tests has been added already in a different CL [2].

[1] https://groups.google.com/a/chromium.org/d/msg/blink-dev/8qesjfh0a80/xrruWrixBwAJ
[2] https://crrev.com/c/1904077

Bug: 905315
Change-Id: I1e78599777436989fefcd988c04074f33cbf452d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1900002
Commit-Queue: Javier Fernandez <jfernandez@igalia.com>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713776}

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -378,7 +378,7 @@
     },
     {
       name: "CSS3TextBreakAnywhere",
-      status: "experimental",
+      status: "stable",
     },
     {
       name: "CSSAdditiveAnimations",