Revert "Remove highlight.js js_component"

This reverts commit a7f0e62938b723556a529e5cba05e5ada0e6aa2b.

The //lib/js:highlightjs in
//polygerrit-ui:polygerrit_components.bower_components appeared to be
unused because the library is specially inserted into the PG app bundle
in polygerrit-ui/app/rules.bzl. However, it was used by development
servers such as the WAR using --polygerrit-dev or by the run-server.sh
proxy.

Bug: Issue 8777
Change-Id: Ie1467ed9bc9f7e011c870629ba1c9390fa0c9559

polygerrit-ui/BUILD

diff --git a/polygerrit-ui/BUILD b/polygerrit-ui/BUILD
index b338cbf..fddfc57 100644
--- a/polygerrit-ui/BUILD
+++ b/polygerrit-ui/BUILD
@@ -11,6 +11,9 @@
         "//lib/js:ba-linkify",
         "//lib/js:es6-promise",
         "//lib/js:fetch",
+        # Although highlightjs is inserted separately in the UI zip, it's used
+        # by local development servers (e.g. --polygerrit-dev or run-server.sh).
+        "//lib/js:highlightjs",
         "//lib/js:iron-a11y-keys-behavior",
         "//lib/js:iron-autogrow-textarea",
         "//lib/js:iron-dropdown",