Import global functions and constants for enhanced performance

This is better for performance because these then don't need to be reevaluated every time they are called.

When encountering an unqualified function or constant reference, PHP will first try to locate a symbol in the current namespace by that name, and then fall back to the global namespace.
This short-circuits the check, which has substantial performance effects in some cases - in particular, ord(), chr() and strlen() show ~1500x faster calls when they are fully qualified.

However, this doesn't mean that PM is getting a massive amount faster. In real world terms, this translates to about 10-15% performance improvement.
But before anyone gets excited, you should know that the CodeOptimizer in the PreProcessor repo has been applying fully-qualified symbol optimizations to Jenkins builds for years, which is one of the reasons why Jenkins builds have better performance than home-built or source installations.
We're choosing to do this for the sake of future SafePHP integration and also to be able to get rid of the buggy CodeOptimizer, so that phar and source are more consistent.

src/pocketmine/Player.php

@@ -160,6 +160,40 @@ use pocketmine\tile\Tile;
 use pocketmine\timings\Timings;
 use pocketmine\utils\TextFormat;
 use pocketmine\utils\UUID;
+use function abs;
+use function array_merge;
+use function assert;
+use function base64_decode;
+use function ceil;
+use function count;
+use function explode;
+use function floor;
+use function fmod;
+use function get_class;
+use function gettype;
+use function implode;
+use function in_array;
+use function is_int;
+use function is_object;
+use function is_string;
+use function json_encode;
+use function json_last_error_msg;
+use function lcg_value;
+use function max;
+use function microtime;
+use function min;
+use function preg_match;
+use function round;
+use function spl_object_hash;
+use function strlen;
+use function strpos;
+use function strtolower;
+use function substr;
+use function trim;
+use function ucfirst;
+use const M_PI;
+use const M_SQRT3;
+use const PHP_INT_MAX;
 
 
 /**