Bug 1543045 - Break strings for long CSS property names and values. r=gl

Introduce `overflow-wrap: break-word` to CSS declarations in Rules view and Changes panel to prevent long strings from causing unwanted horizontal scroll

Differential Revision: https://phabricator.services.mozilla.com/D27120

--HG--
extra : moz-landing-system : lando

devtools/client/themes/changes.css

@@ -145,6 +145,10 @@
   display: block;
 }
 
+.changes__declaration {
+  overflow-wrap: break-word;
+}
+
 .changes__declaration-name {
   margin-left: 10px;
 }

devtools/client/themes/rules.css

@@ -567,6 +567,7 @@
   border-left: 3px solid transparent;
   clear: both;
   padding-left: 28px;
+  overflow-wrap: break-word;
 }
 
 .ruleview-propertycontainer  > * {