Add group_to_single_imports option to single_import_per_statement

[paulbalandan]

Description

$ vendor/bin/php-cs-fixer describe single_import_per_statement
Description of single_import_per_statement rule.
There MUST be one use keyword per declaration.

Fixer is configurable using following option:
* group_to_single_imports (bool): whether to change group imports into single imports; defaults to true

Fixing examples:
 * Example #1. Fixing with the default configuration.
   ---------- begin diff ----------
   --- Original
   +++ New
   @@ -1,2 +1,4 @@
    <?php
   -use Foo, Sample, Sample\Sample as Sample2;
   +use Foo;
   +use Sample;
   +use Sample\Sample as Sample2;

   ----------- end diff -----------

 * Example #2. Fixing with configuration: ['group_to_single_imports' => true].
   ---------- begin diff ----------
   --- Original
   +++ New
   @@ -1,6 +1,4 @@
    <?php
   -use Space\Models\ {
   -    TestModelA,
   -    TestModelB,
   -    TestModel,
   -};
   +use Space\Models\TestModelA;
   +use Space\Models\TestModelB;
   +use Space\Models\TestModel;

   ----------- end diff -----------

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide