Add predefined operationId support.

[tibortakacs]

If the operation described in the XML file has an <operationId> tag, it is used, otherwise (keeping the original behaviour) the id is generated using the path () and the operation type ().

In order to do this, the following changes have been introduced:

• Add UsePredefinedOperationIdFilter class which creates operations using <operationId> tag.

• Add CreateOperationMetaFilter which executes a list of operation creation filters. The first successful filter is used to generate the operations. This mechanism is used to support both the predefined and the generated operation id: first, the predefined operation id based filter is used, and if it fails, the operation id generation based filter is executed.

• Add ICreateOperationPreprocessingOperationFilter to support applicable check in operation create filters in a general way.

• Extend OperationHandler with GetOperationId function.

• Slight refactor.

• Small fix in GetUrl function.

• Add extensive unit tests

• Remove duplicated code from BranchOptionalPathParametersFilter and use OperationHandler existing functionality.

[tonymadkins]

This would be very useful for the MCAPI Fulfillment team! We are generating our OpenAPI spec with this package and found the operationId tag is consumed directly by the Geneva Actions extension when onboarding with their portal, so we could really use a customizable operationId tag to provide a more readable extension for our APIs.