Improve default failed equality match output to more clearly show diffs

[takaaa220]

Hi, maintainers! I would like to express my sincere gratitude for your efforts in maintaining gomock.

Requested feature
Is the issue golang/mock#616 resolved? If not, i hope improvement the diffs when tests fails.

I didn't find out whether the problem resolved or not as the original repository has the issue archived and cannot ask there.

Why the feature is needed
As showing the original issue, it is often hard to understand and interpret the diffs.

(Optional) Proposed solution
i think we can solve this problem by using the method indicated in the following comments:

• Improve default failed equality match output to more clearly show diffs golang/mock#616 (comment)
• Improve default failed equality match output to more clearly show diffs golang/mock#616 (comment)

Alternatively, adding an option to change the default matcher may resolve this, as it would allow for the use of this way.

[tmc]

The current diff output is pretty low readability. Would love to see the golang/mock#616 (comment) or something similar implemented.