Feature Request: use client constructors' `options.projectId` as default project ID for client methods

[mscdex]

(Originally from https://github.com/googleapis/nodejs-compute/issues/790)

Is your feature request related to a problem? Please describe. It's annoying to have to pass projectId to every client method if the project ID never changes for the particular client instance.

Describe the solution you'd like Have client methods default to options.projectId passed to the client constructor when an explicit project is not passed to client methods.

Describe alternatives you've considered Flipping a table.