Clean up Phabricator interface to syntax highlighting

Summary: Reduce the amount of code duplication here and allow for an override
configuration on the filename.map stuff.
Test Plan: Checked paste, diffusion and differential syntax highlighting and
everything appeared reasonable.
Reviewed By: codeblock
Reviewers: tuomaspelkonen, codeblock, jungejason, aran
CC: aran, codeblock, epriestley
Differential Revision: 601

src/applications/differential/parser/changeset/DifferentialChangesetParser.php

@@ -873,10 +873,7 @@ EOSYNTHETIC;
     $this->isTopLevel = (($range_start === null) && ($range_len === null));
 
 
-    $this->highlightEngine = new PhutilDefaultSyntaxHighlighterEngine();
-    $this->highlightEngine->setConfig(
-      'pygments.enabled',
-      PhabricatorEnv::getEnvConfig('pygments.enabled'));
+    $this->highlightEngine = PhabricatorSyntaxHighlighter::newEngine();
 
     $this->tryCacheStuff();