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

(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.