Description:
------------
According to IANA Asia/Rangoon is only a link for Asia/Yangon.
The function timezone_identifiers_list returns only Asia/Rangoon.

The documentation of the function does not specifies that it's going to return only some of the available ids so the user expectation is to have at least main ids, instead of secondary linked ones.

A documentation change would make easy to understand what the function returns.
And also all of the primary ids should be returned.

Test script:
---------------
<?php

if (!in_array('Asia\Yangon', timezone_identifiers_list())) {
    echo 'Asia\Yangon not returned';
}

if (!in_array('Asia\Rangoon', timezone_identifiers_list())) {
    echo PHP_EOL . 'Asia\Rangoon returned';
}



Expected result:
----------------
# if the intent of the function is to return only IANA primary ids

Asia\Yangon returned
Asia\Rangoon not returned 

# else if the intent of the function is to return all of the ids


Asia\Yangon returned
Asia\Rangoon returned 


Actual result:
--------------
Asia\Yangon not returned
Asia\Rangoon returned