Replace array_shift() with current() where appropriate

[SergeyBiryukov]

Background: #31182

array_shift() recalculates array indexes, and can be slow on large arrays. Most of the time, this is unnecessary, as we only use it to get the first element of the array, and the array is never used later.

[SergeyBiryukov]

Related: #31260

[wonderboymusic]

Yes, array_shift() does a lot:
​https://github.com/php/php-src/blob/745504ea2a7066588af9714f5e32523a3fff4db7/ext/standard/array.c#L2199

I tend to prefer reset() over current(), because reset() is guaranteed to be the first item, while current() is based on the pointer at calltime. Internally, they are basically the same.

reset()
​https://github.com/php/php-src/blob/745504ea2a7066588af9714f5e32523a3fff4db7/ext/standard/array.c#L889

current()
​https://github.com/php/php-src/blob/745504ea2a7066588af9714f5e32523a3fff4db7/ext/standard/array.c#L922

[nacin]

Strongly agree on not depending on the pointer being the first item.

This is definitely not the first time we've converted array modification functions to reset() and such. They sneak in over time.

[wonderboymusic]

In 31829:

Replace array_shift() with reset() where appropriate for performance.

Props SergeyBiryukov.
Fixes #31259.

[SergeyBiryukov]

In 31841:

After [31730], replace one more instance of array_shift() with reset() for better performance.

see #31259, #15459.

[SergeyBiryukov]

In 31842:

Bundled themes: After [31453], replace current() with reset(), which is guaranteed to be the first item.

see #31259, #31260.