[11.x] PHPDoc Improvements

[schulerj89]

Update the PHPDoc to the Arr::exists function to show it also accepts float as a param value

> Arr::exists(['1.2' => 1], 1.2);
= true

[rodrigopedra]

At first, I thought on arguing against this PR, as one could say to also add boolean to the list:

> Arr::exists([1 => 1], true)
= true

But after looking into the source, the Arr::exists() explicitly checks if the key is a float, thus behaving differently from the array_key_exists() PHP function, which would truncate the float to an integer.

framework/src/Illuminate/Collections/Arr.php

Lines 164 to 179 in 8fbb940

	public static function exists($array, $key)
	{
	if ($array instanceof Enumerable) {
	return $array->has($key);
	}
	if ($array instanceof ArrayAccess) {
	return $array->offsetExists($key);
	}
	if (is_float($key)) {
	$key = (string) $key;
	}
	return array_key_exists($key, $array);
	}

As such, I guess it is best to add the type hint.