Modify get_template_part() to include sub folder path

[dgwyer]

I have been using more and more template parts, that I include into my main theme template files, using get_template_part().

It would be great if it was possible to tidy up the theme root folder by placing all template parts in a sub folder.

I have attached a modified get_template_part() function with the proposed changes.

[scribu]

#15086