✨Support XValidation on type aliases to map/slice/pointer types

[dongjiang1989]

What does this PR do, and why do we need it?

Fixes #1462

controller-gen did not generate x-kubernetes-validations for type aliases to complex types (e.g. type X = map[string]string). The alias was unwrapped to the underlying type in localNamedToSchema, which hit the default case and produced an error:

unsupported type *types.Map for identifier X

Changes

For user-defined type aliases (type X = Y) whose RHS is a non-basic, non-named type (map, slice, pointer, etc.), emit a $ref to the alias type instead of unwrapping it. The flattener then resolves the $ref via infoToSchema, which correctly applies markers on the alias declaration (including +kubebuilder:validation:XValidation).

Behavior for other alias types is preserved:

• Basic type aliases (type X = string): unwrap, emit inline type/format + $ref (preserves field-level markers like MinLength/MaxLength)
• Named type aliases (type X = SomeStruct): unwrap, emit $ref to the underlying named type (preserves inline/embedded struct alias behavior and applyconfiguration generator compatibility)
• Built-in aliases (any): unwrap (no $ref, since any is not a user-defined type)

Example

// +kubebuilder:validation:XValidation:rule=`self.all(key, size(key) > 0)`,message="keys must be non-empty"
type Labels = map[string]string

type MySpec struct {
    Labels Labels `json:"labels,omitempty"`
}

Now correctly generates:

labels:
  additionalProperties:
    type: string
  type: object
  x-kubernetes-validations:
  - message: keys must be non-empty
    rule: self.all(key, size(key) > 0)

[kubernetes-prow]

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[dongjiang1989]

cc @sbueringer PTAL, thanks