API Machinery: Add equal func for Requirement struct

[gavinfish]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Add Equal func for Requirement struct. This is useful when we need compare Requirement and Selector with cmp lib.

Which issue(s) this PR fixes:

Xref #94696

Special notes for your reviewer:

Does this PR introduce a user-facing change?

none

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[gavinfish]

/assign @caesarxuchao

[fedebongio]

/triage accepted

[caesarxuchao]

Curious in what respects cmp.Equal works better than reflect.DeepEqual for internalSelector? Can you make an example?

Anyway, this PR looks good.

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[gavinfish]

Curious in what respects cmp.Equal works better than reflect.DeepEqual for internalSelector? Can you make an example?

Anyway, this PR looks good.

/lgtm
/approve

For internalSelector, there is no big difference since all fields matter. But for other structs holding Selector(internalSelector) as a field, we need use AllowUnexporterted (most time this is not what we want as it acts similarly as reflect.DeepEqual) option or deliberately implement an Equal func dealing with Selector when we use cmp lib.