Unified resource types

Rules for AIP-123, covering unified resource types.

Rule name	Description
`duplicate-resource`	Resource types should not be defined more than once.
`name-never-optional`	Resource name fields must never be labeled with proto3_optional.
`resource-annotation`	Resource messages should be annotated with `google.api.resource`.
`resource-definition-pattern`	Resource annotations should define a pattern.
`resource-definition-type-name`	Resource type names must be of the form {Service Name}/{Type}.
`resource-definition-variables`	Resource patterns should use consistent variable naming.
`resource-name-components-alternate`	Resource name components should alternate between collection and identifiers.
`resource-name-field`	Resource messages should have a `string name` field.
`resource-pattern`	Resource annotations should define a pattern.
`resource-pattern-plural`	Resource patterns must use the plural as the collection segment
`resource-pattern-singular`	Resource patterns must use the singular as the resource ID segment
`resource-plural`	Resource plural is required
`resource-reference-type`	Resource reference annotations should only apply to strings.
`resource-singular`	Resource singular is required and must be lowerCamelCase of type
`resource-type-message`	Resource type names must match containing message name.
`resource-type-name`	Resource type names must be of the form {Service Name}/{Type}.
`resource-variables`	Resource patterns should use consistent variable naming.

Note: Because AIPs sometimes cover topics that have some overlap, some rules related to unified resource types may be included in the rules for other AIPs.