This commit moves the build-related scripts
(`build-ivy-npm-packages.js`, `build-packages-dist.js` and
`package-builder.js`) to a dedicated directory to keep the `scripts/`
directory cleaner.
It also moves the logic for building the `zone.js` package to a separate
script, `zone-js-builder.js`, to make it re-usable. A subsequent commit
will use it to build the `zone.js` package when building the Ivy Angular
packages as well.
PR Close#35780
In #33823, `scripts/package-builds.sh` (which is used by both
`build-packages-dist.sh` and `build-ivy-npm-packages.sh`) was updated to
use `realpath`. It turns out that `realpath` does not exist on macOS, so
the build scripts do not work there.
In order to fix this (and also reduce the likelihood of introducing
similar issues in the future), this commit changes these bash scripts to
Node.js scripts (using [ShellJS](https://github.com/shelljs/shelljs) for
a cross-platform implementation of Unix shell commands where necessary).
PR Close#33854