Summary

Configuring the file extensions for Handlebars syntax highlighting does not take affect and the text does not receive any highlighting. 

Steps to Reproduce

1. In bitbucket.properties add syntax.highlighter.text/x-handlebars-template.extensions=hbs
2. Restart Bitbucket Server
3. Add the below code to a test.hbs file, commit, and push it to a repository
4. Browse to the file

   {{> breadcrumbs}}
   
   {{!--
    You can use the t function to get
    content translated to the current locale, es:
    {{t 'article_list'}}
   --}}
   
   <h1>{{t 'article_list'}}</h1>
   
   {{! one line comment }}
   
   {{#each articles}}
    {{~title}}
    <p>{{excerpt body size=120 ellipsis=true}}</p>
   
    {{#with author}}
    written by {{first_name}} {{last_name}}
    from category: {{../category.title}}
    {{#if @../last}}foobar!{{/if}}
    {{/with~}}
   
    {{#if promoted.latest}}Read this one! {{else}} This is ok! {{/if}}
   
    {{#if @last}}<hr>{{/if}}
   {{/each}}
   
   {{#form new_comment}}
    <input type="text" name="body">
   {{/form}}
   

Expected Results

Code is highlighted as seen on https://codemirror.net/mode/handlebars/index.html

Actual Results

Code is not highlighted