New function: `template_directory_uri()`

[sebastian.pisula]

Display theme directory URI.

For example:

<img src="<?php template_directory_uri();?>/images/separator.png" />

[swissspidy]

First, you should always escape such output, e.g. by using echo esc_url( get_template_directory_uri() . '/images/separator.png' ). With your proposed patch, that would not work and I'd highly discourage to use that.

Second, why limit this to get_template_directory_uri() and not also add a similar function for get_stylesheet_directory_uri()?

[DrewAPicture]

Duplicate of #30797.