Add helper functions for resource path construction for all resource patterns

[parthea]

There is a limitation in the resource_path method of gapic.schema.wrappers where it only returns the first resource path and ignores others. When https://github.com/googleapis/gapic-generator-python/issues/242 was implemented, helper functions were only created for the first resource path. We should consider creating helper functions for all resource paths rather than just the first one to improve the experience for users.

https://github.com/googleapis/gapic-generator-python/blob/8d6a035f2c91cab0bc9fad25b7c0af5c5bfa63af/gapic/schema/wrappers.py#L593-L600