[Fix #8283] Fix length calculation for Style/IfUnlessModifier

[dmytro-savochkin]

Fixes #8283.
Fixes #8226.
Fixes #8025, #8006, #7969 (look like duplicates).

1. The code to calculate line length for Style/IfUnlessModifier when considering conversion to single-line form now uses the same method that actually computes the replacement. This allows us to take into account a comment on a first line of the if-end condition or some code that is on the same line before the if-condition (which both contribute to the line length).
2. Added code so that if-end condition that is either an element of an array or a value of a hash now correctly converted to a single-line form with parentheses.

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[bbatsov]

The changes look good to me. Thanks!

[AlexWayfer]

Thank you! ❤️