tighten validation of inlining and metadata

[pohly]

This catches the following mistake:

type ResourceSliceList struct {
   metav1.ListMeta `json:"listMeta" protobuf:"bytes,1,opt,name=listMeta"`
   ...
}

The "listMeta" name matches the Go field name, but the convention is to call that JSON field "metadata".

The same applies to ObjectMeta.

While at it, usage of the empty JSON name also gets checked more thoroughly. This is a mistake which was not detected earlier:

type SomeStruct struct {
    SomeInt int `json:",inline"`
}

[liggitt]

/lgtm /approve

[pohly]

Using this in Kubernetes might be tricky, updating the dependency wasn't straight-forward - see https://github.com/kubernetes/kubernetes/pull/126917 (not including this PR yet).

[liggitt]

~try rebasing, some other fixups went in last week (https://github.com/kubernetes/kube-openapi/pull/507, https://github.com/kubernetes/kube-openapi/pull/508)~

I'd recommend waiting until https://github.com/kubernetes/kubernetes/pull/126787 gets in and handles the regen cleanup

[liggitt]

/lgtm

[Jefftree]

/lgtm /approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Jefftree, liggitt, pohly

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