define methods, types, and unit tests for transformer annotations

[natasha41575]

Defining some types and methods that will be necessary for the implementation of the transformer annotation proposal.

Added unit tests for new methods as well as for methods defined in #4341.

As described in #4267 (comment), in order to account for the case where there is a generator in the transformers field, we will add an origin annotation when there is none - i.e. assume that the transformer generated the resource; otherwise we will add a transformer annotation. In order for this to work, we will have to keep track of both the origin and the transformer data when either option is set. At the end of kustomize build, if only one of the origin or transformer options is set, we need to discard the other annotation. This will be taken care of by a future PR, but this context is needed to understand the implementation of resWrangler.AddTransformerAnnotation and is the reason for introducing ResMap.RemoveOriginAnnotations() and ResMap.RemoveTransformerAnnotations().

A followup PR will use these new types and methods to track and annotate each resource with transformer data.

/cc @KnVerey
/cc @yuwenma

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[natasha41575]

ping @yuwenma

[yuwenma]

/lgtm
nice PR