fix deep equal check failure on objects with runtime.RawExtension.

[zach593]

What type of PR is this?
/kind bug

What this PR does / why we need it:
see #5938

Which issue(s) this PR fixes:
Fixes #5938

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

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Codecov Report

Attention: Patch coverage is 27.65957% with 34 lines in your changes missing coverage. Please review.

Project coverage is 48.15%. Comparing base (a6df137) to head (a59f918).
Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/util/equality.go	33.33%	23 Missing and 3 partials ⚠️
cmd/agent/app/agent.go	0.00%	4 Missing ⚠️
cmd/controller-manager/app/controllermanager.go	0.00%	4 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5940      +/-   ##
==========================================
+ Coverage   48.09%   48.15%   +0.06%     
==========================================
  Files         663      665       +2     
  Lines       54769    54850      +81     
==========================================
+ Hits        26340    26415      +75     
+ Misses      26719    26717       -2     
- Partials     1710     1718       +8     

Flag	Coverage Δ
unittests	48.15% <27.65%> (+0.06%)	⬆️

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[zhzhuang-zju]

Should we consider the case where a.Raw is nil or an empty byte array?

	obj1 := &workv1alpha1.Work{
		Spec: workv1alpha1.WorkSpec{
			Workload: workv1alpha1.WorkloadTemplate{Manifests: []workv1alpha1.Manifest{{RawExtension: runtime.RawExtension{Raw: []byte{}}}}},
		},
	}
	obj2 := &workv1alpha1.Work{
		Spec: workv1alpha1.WorkSpec{
			Workload: workv1alpha1.WorkloadTemplate{Manifests: []workv1alpha1.Manifest{{RawExtension: runtime.RawExtension{Raw: nil}}}},
		},
	}
	checker := equality.Semantic.Copy()
	_ = RegisterEqualityCheckFunctions(&checker)
	fmt.Println(equality.Semantic.DeepEqual(obj1, obj2)) #true
	fmt.Println(checker.DeepEqual(obj1, obj2)) #false

[zhzhuang-zju]

How about

Suggested change

	var aObj, bObj unstructured.Unstructured
	err := aObj.UnmarshalJSON(a.Raw)
	if err != nil {
	return false
	}
	err = bObj.UnmarshalJSON(b.Raw)
	if err != nil {
	if (a.Raw == nil || len(a.Raw) == 0) != (b.Raw == nil || len(b.Raw) == 0) {
	return false
	}
	if a.Raw == nil || len(a.Raw) == 0 {
	return true
	}
	var aObj, bObj unstructured.Unstructured
	err := aObj.UnmarshalJSON(a.Raw)
	if err != nil {
	return false
	}
	err = bObj.UnmarshalJSON(b.Raw)
	if err != nil {