Fix/to equal undefined comparison

[STAR-173]

Fixes #7083

Description

This PR fixes the toEqual matcher to consistently ignore undefined properties when comparing objects. Previously, undefined properties were inconsistently highlighted in error messages, leading to confusion. The fix ensures predictable behavior and clearer error messages. Unit tests have been added to validate the changes.

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[STAR-173]

Hey @hi-ogawa ,
There are some test which are failing now which never failed before. Also, they are failing on the main branch.
Do you have any idea on this ?