Extract conflict detection to it's own interface.

This PR
 - defines a patch conflict detector interface,
 - extracts implementations of the interface from the
   merginator code, making the merginator code
   independent of --enable_kyaml.
 - injects those implementations into kustomize
   as a function of --enable_kyaml.

So, instead of using different merginators to combine
resmaps, this pr allows the use of a single patch merge
code path that uses different conflict detectors.

So instead of debating how to merge, we're now only
considering whether to warn on conflict detection
in one transformer.

This PR is in service of #3304, eliminating seven
instances where --enable_kyaml was consulted.  These
were cases where conflict detection wasn't an issue
(but merging patches was).

api/provider/depprovider.go

@@ -5,14 +5,13 @@ package provider
 
 import (
 	"sigs.k8s.io/kustomize/api/ifc"
-	"sigs.k8s.io/kustomize/api/internal/k8sdeps/merge"
-	kmerge "sigs.k8s.io/kustomize/api/internal/merge"
+	"sigs.k8s.io/kustomize/api/internal/conflict"
+	k8sconflict "sigs.k8s.io/kustomize/api/internal/k8sdeps/conflict"
 	"sigs.k8s.io/kustomize/api/internal/validate"
 	"sigs.k8s.io/kustomize/api/internal/wrappy"
 	"sigs.k8s.io/kustomize/api/k8sdeps/kunstruct"
 	"sigs.k8s.io/kustomize/api/k8sdeps/validator"
 	"sigs.k8s.io/kustomize/api/konfig"
-	"sigs.k8s.io/kustomize/api/resmap"
 	"sigs.k8s.io/kustomize/api/resource"
 )
 
@@ -96,17 +95,27 @@ import (
 //            would really reduce the work
 //            (e.g. drop Vars, drop ReplacementTranformer).
 //
-//   - resmap.Merginator
+//   - resource.ConflictDetector
 //
-//       1) api/internal/k8sdeps/merge.Merginator
+//       1) api/internal/k8sdeps/conflict.conflictDetectorJson
+//          api/internal/k8sdeps/conflict.conflictDetectorSm
 //
 //            Uses k8s.io/apimachinery/pkg/util/strategicpatch,
 //            apimachinery/pkg/util/mergepatch, etc. to merge
 //            resource.Resource instances.
 //
-//       2) api/internal/merge.Merginator
+//       2) api/internal/conflict.smPatchMergeOnlyDetector
 //
-//            At time of writing, this is unimplemented.
+//           At time of writing, this doesn't report conflicts,
+//           but it does know how to merge patches. Conflict
+//           reporting isn't vital to kustomize function.  It's
+//           rare that a person would configure one transformer
+//           with many patches, much less so many that it became
+//           hard to spot conflicts.  In the case of an undetected
+//           conflict, the last patch applied wins, likely what
+//           the user wants anyway.  Regardless, the effect of this
+//           is plainly visible and usable in the output, even if
+//           a conflict happened but wasn't reported as an error.
 //
 //   - ifc.Validator
 //
@@ -117,6 +126,7 @@ import (
 //
 //       2) api/internal/validate.FieldValidator
 //
+//            See TODO inside the validator for status.
 //            At time of writing, this is a do-nothing
 //            validator as it's not critical to kustomize function.
 //
@@ -139,20 +149,20 @@ import (
 // If you're reading this, plan not done.
 //
 type DepProvider struct {
-	kFactory        ifc.KunstructuredFactory
-	resourceFactory *resource.Factory
-	merginator      resmap.Merginator
-	fieldValidator  ifc.Validator
+	kFactory                 ifc.KunstructuredFactory
+	resourceFactory          *resource.Factory
+	conflictDectectorFactory resource.ConflictDetectorFactory
+	fieldValidator           ifc.Validator
 }
 
 func makeK8sdepBasedInstances() *DepProvider {
 	kf := kunstruct.NewKunstructuredFactoryImpl()
 	rf := resource.NewFactory(kf)
 	return &DepProvider{
-		kFactory:        kf,
-		resourceFactory: rf,
-		merginator:      merge.NewMerginator(rf),
-		fieldValidator:  validator.NewKustValidator(),
+		kFactory:                 kf,
+		resourceFactory:          rf,
+		conflictDectectorFactory: k8sconflict.NewFactory(rf),
+		fieldValidator:           validator.NewKustValidator(),
 	}
 }
 
@@ -160,10 +170,10 @@ func makeKyamlBasedInstances() *DepProvider {
 	kf := &wrappy.WNodeFactory{}
 	rf := resource.NewFactory(kf)
 	return &DepProvider{
-		kFactory:        kf,
-		resourceFactory: rf,
-		merginator:      kmerge.NewMerginator(rf),
-		fieldValidator:  validate.NewFieldValidator(),
+		kFactory:                 kf,
+		resourceFactory:          rf,
+		conflictDectectorFactory: conflict.NewFactory(),
+		fieldValidator:           validate.NewFieldValidator(),
 	}
 }
 
@@ -186,8 +196,8 @@ func (dp *DepProvider) GetResourceFactory() *resource.Factory {
 	return dp.resourceFactory
 }
 
-func (dp *DepProvider) GetMerginator() resmap.Merginator {
-	return dp.merginator
+func (dp *DepProvider) GetConflictDetectorFactory() resource.ConflictDetectorFactory {
+	return dp.conflictDectectorFactory
 }
 
 func (dp *DepProvider) GetFieldValidator() ifc.Validator {