Improve word breaking in doc table

To maintain similar word breaking without adding <wbr> tags I've added
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

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 {