minor #4049 use parent::offset*() methods when moving items arround in insertAt() (staabm)
minor #4049 use parent::offset*() methods when moving items arround in insertAt() (staabm)

This PR was squashed before being merged into the 2.12 branch (closes #4049).

Discussion
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use parent::offset*() methods when moving items arround in insertAt()

since we only move already existing items arround, we directly call into SplFixedArray::offset* methods.

that way we get arround additional overhead Tokens class adds with overridden offset* methods.

blackfire shows a 35-40% runtime improvement in overall walltime.
in my testbenchmark this renders a ~20 second improvement.

https://blackfire.io/profiles/compare/4a0c1058-5910-446d-9641-8bcf2823cc63/graph

![image](https://user-images.githubusercontent.com/120441/47035734-06cbc400-d17b-11e8-8dd6-badf56512bd1.png)

Commits
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2905d496 use parent::offset*() methods when moving items arround in insertAt()

GrahamCampbell/PHP-CS-Fixer,GrahamCampbell/PHP-CS-Fixer,kubawerlos/PHP-CS-Fixer,Slamdunk/PHP-CS-Fixer,FriendsOfPHP/PHP-CS-Fixer,kubawerlos/PHP-CS-Fixer,gharlan/PHP-CS-Fixer,SpacePossum/PHP-CS-Fixer,FriendsOfPHP/PHP-CS-Fixer,keradus/PHP-CS-Fixer,SpacePossum/PHP-CS-Fixer,keradus/PHP-CS-Fixer,gharlan/PHP-CS-Fixer,Slamdunk/PHP-CS-Fixer