Improve the performance of emoji iteration in `wp_encode_emoji()` and `wp_staticize_emoji()`

[johnbillion]

The wp_encode_emoji() and wp_staticize_emoji() functions perform a version comparison against the PHP version for every emoji that they iterate over - currently either 1,250 or 2,839 depending on whether the partial or full list of emoji are being iterated.

This behaviour was introduced in [41702].

By moving the PHP version comparison out of the loop, those thousands of comparisons are avoided and the processing time of both functions are reduced by approximately 50%.

1,000 iterations of wp_encode_emoji() before the proposed change: 4.0 seconds.
1,000 iterations of wp_encode_emoji() after the proposed change: 1.9 seconds.

[pento]

Noice. 🙂

If WordPress 5.2 is going to drop PHP<5.6 support, not much point waiting until then, so let's do this in 5.1.

[pento]

In 44554:

Emoji: Improve performance when encoding or staticizing emoji.

Both wp_encode_emoji() and wp_staticize_emoji() perform a PHP version check when deciding how to apply their behaviour, but this check only needs to happen once, rather than every time in their internal looks.

Moving the check outside of the loop reduces processing time by 50%.

Props johnbillion.
Fixes #45930.

[pento]

In 44556:

Emoji: Fix a code formatting error introduced in [44554].

See #45930.