Bug 1719535 - Part 11. Enable icu4x segmenter on Nightly. r=platform-i18n-reviewers,dminor,jfkthame

Depends on D167678

Differential Revision: https://phabricator.services.mozilla.com/D167745

modules/libpref/init/StaticPrefList.yaml

@@ -7295,7 +7295,7 @@
 # If true, we use UAX14/29 compatible segmenter rules using ICU4X
 - name: intl.icu4x.segmenter.enabled
   type: RelaxedAtomicBool
-  value: false
+  value: @IS_NIGHTLY_BUILD@
   mirror: always
 
 #---------------------------------------------------------------------------