build: move build scripts to dedicated directory (#35780)

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

.circleci/config.yml

@@ -520,7 +520,7 @@ jobs:
     steps:
       - custom_attach_workspace
       - init_environment
-      - run: node scripts/build-packages-dist.js
+      - run: node scripts/build/build-packages-dist.js
 
       # Save the npm packages from //packages/... for other workflow jobs to read
       - persist_to_workspace:
@@ -545,7 +545,7 @@ jobs:
     steps:
       - custom_attach_workspace
       - init_environment
-      - run: node scripts/build-ivy-npm-packages.js
+      - run: node scripts/build/build-ivy-npm-packages.js
 
       # Save the npm packages from //packages/... for other workflow jobs to read
       - persist_to_workspace: