Adopt PSR-12 for imports statements separation

[PSR-12](https://www.php-fig.org/psr/psr-12) is an extension of the PSR-2 set of rules
that aims to standardize the code style.

As per PSR-12, under the [item 3](https://www.php-fig.org/psr/psr-12/#3-declare-statements-namespace-and-import-statements):

The header of a PHP file may consist of a number of different blocks. If present,
each of the blocks below MUST be separated by a single blank line, and MUST NOT
contain a blank line. Each block MUST be in the order listed below, although
blocks that are not relevant may be omitted.

For context on why this was voted in the past, see #9.

lib/Doctrine/ruleset.xml

@@ -301,7 +301,7 @@
         <properties>
             <property name="linesCountAfterLastUse" value="1"/>
             <property name="linesCountBeforeFirstUse" value="1"/>
-            <property name="linesCountBetweenUseTypes" value="0"/>
+            <property name="linesCountBetweenUseTypes" value="1"/>
         </properties>
     </rule>
     <!-- Forbid useless alias for classes, constants and functions -->

tests/fixed/ControlStructures.php

@@ -6,6 +6,7 @@
 
 use InvalidArgumentException;
 use Throwable;
+
 use const PHP_VERSION;
 
 class ControlStructures

tests/fixed/example-class.php

@@ -9,9 +9,11 @@
 use Fancy\TestCase;
 use InvalidArgumentException;
 use IteratorAggregate;
+
 use function assert;
 use function strlen as stringLength;
 use function substr;
+
 use const PHP_MINOR_VERSION;
 use const PHP_RELEASE_VERSION as PHP_PATCH_VERSION;
 use const PHP_VERSION;

tests/fixed/namespaces-spacing.php

@@ -7,8 +7,10 @@
 use DateInterval;
 use DateTimeImmutable;
 use DateTimeZone;
+
 use function strrev;
 use function time;
+
 use const DATE_RFC3339;
 
 strrev(

tests/fixed/use-ordering.php

@@ -6,7 +6,9 @@
 
 use DateTimeImmutable;
 use DateTimeInterface;
+
 use function sprintf;
+
 use const PHP_EOL;
 
 echo sprintf('Current date and time is %s', (new DateTimeImmutable())->format(DateTimeInterface::ATOM)) . PHP_EOL;

tests/input/ControlStructures.php

@@ -6,6 +6,7 @@
 
 use InvalidArgumentException;
 use Throwable;
+
 use const PHP_VERSION;
 
 class ControlStructures

tests/input/example-class.php

@@ -5,9 +5,13 @@
 namespace Example;
 
 use Throwable;
+
 use function strlen as stringLength;
+
 use Fancy\TestCase as TestCase;
+
 use const PHP_RELEASE_VERSION as PHP_PATCH_VERSION;
+
 use Doctrine\Sniffs\Spacing\ControlStructureSniff;
 
 /**

tests/input/namespaces-spacing.php

@@ -5,10 +5,8 @@
 use DateInterval;
 use DateTimeImmutable;
 use DateTimeZone;
-
 use function strrev;
 use function time;
-
 use const DATE_RFC3339;
 strrev(
     (new DateTimeImmutable('@' . time(), new DateTimeZone('UTC')))

tests/input/use-ordering.php

@@ -5,8 +5,11 @@
 namespace Foo;
 
 use function sprintf;
+
 use DateTimeImmutable;
+
 use const PHP_EOL;
+
 use DateTimeInterface;
 
 echo sprintf('Current date and time is %s', (new DateTimeImmutable())->format(DateTimeInterface::ATOM)) . PHP_EOL;