chore(ci): copy deployment files inside the respective Firebase directories

We have the `scripts/{code,docs}.angularjs.org-firebase/` directories,
which contain the necessary code and config for deploying built files to
the `code-angularjs-org` and `docs-angularjs-org` Firebase projects
respectively.

Previously, some of the files that needed to be deployed to Firebase (or
Google Cloud) were placed outside these directories (e.g. in
`deploy/{code,docs}/`).

Since these files are only used for deploying to Firebase/Google Cloud,
this commit changes the deployment process to instead copy the files
inside the directories. In a subsequent commit, this will allow
simplifying the deployment process, by running it from inside each
directory instead of having to copy the `firebase.json` files to the
repository root (and adjust the paths).

These are the destination directory changes:

| Before       | After                                       |
|--------------|---------------------------------------------|
| deploy/code/ | scripts/code.angularjs.org-firebase/deploy/ |
| deploy/docs/ | scripts/docs.angularjs.org-firebase/deploy/ |