Speed up rendering of large docs in doc table (#9014)

Back in 2014 a utility was added to insert <wbr> (word break opportunity)
tags into doc table fields to improve their display in the browser. This
utility looped over every character in _source when it was selected as a
column in the doc table, which it was be default. That really started to
slow things down when displaying large docs. We can maintain similar word 
breaking without adding <wbr> tags by adding some css styles that 
do essentially the same job. word-break: break-word gives us the best 
formatting but it's not a part of the standard yet (see link below) so I 
provided an almost-as-good fallback with break-all.

https://bugs.chromium.org/p/chromium/issues/detail?id=492202#c21

Fixes #6328
Related #1993

src/ui/public/doc_table/components/table_row.js

@@ -1,6 +1,5 @@
 import _ from 'lodash';
 import $ from 'jquery';
-import addWordBreaks from 'ui/utils/add_word_breaks';
 import 'ui/highlight';
 import 'ui/highlight/highlight_tags';
 import 'ui/doc_viewer';
@@ -150,18 +149,14 @@ module.directive('kbnTableRow', function ($compile) {
       /**
        * Fill an element with the value of a field
        */
-      function _displayField(row, fieldName, breakWords) {
+      function _displayField(row, fieldName, truncate) {
         let indexPattern = $scope.indexPattern;
         let text = indexPattern.formatField(row, fieldName);
 
-        if (breakWords) {
-          text = addWordBreaks(text, MIN_LINE_LENGTH);
-
-          if (text.length > MIN_LINE_LENGTH) {
-            return truncateByHeightTemplate({
-              body: text
-            });
-          }
+        if (truncate && text.length > MIN_LINE_LENGTH) {
+          return truncateByHeightTemplate({
+            body: text
+          });
         }
 
         return text;

src/ui/public/doc_table/doc_table.less

@@ -6,6 +6,16 @@ doc-table {
 
   .discover-table-datafield {
     white-space: pre-wrap;
+
+    // break-word is what we really want but it hasn't been added to the standard and adopted by all browsers yet,
+    // so we provide break-all as a fallback
+    word-break: break-all;
+    word-break: break-word;
+  }
+
+  .discover-table-sourcefield {
+    word-break: break-all;
+    word-break: break-word;
   }
 
   .loading {