build(docs-infra): simplify ExampleZipper by removing PackageJsonCustomizer (#38192)

Previously, `ExampleZipper` (the tool used for creating ZIP archives
from our docs examples) used the `PackageJsonCustomizer` to generate
`package.json` files for each example type. This had the following
drawbacks:
- The generated files had to be kept up-to-date with the corresponding
  boilerplate files in `aio/tools/examples/shared/boilerplate/` and
  there was no easy way to find out when the files got out-of-sync.
- The `PackageJsonCustomizer` logic was non-trivial and difficult to
  reason about.
- The same information was duplicated in the boilerplate files and the
  customizer configuration files.

This setup was useful when we used a single `package.json` file for all
docs examples. Now, however, each example type can have its own
boilerplate `package.json` file, including scripts and dependencies
relevant to the example type. Therefore, it is no longer necessary to
generate `package.json` files for ZIP archives.

This commit eliminates the drawbacks mentioned above and simplifies the
`ExampleZipper` tool by removing `PackageJsonCustomizer` and re-using
the boilerplate `package.json` files for ZIP archives.

The changes in this commit also fix some ZIP archives that were
previously broken (for example due to missing dependencies).

PR Close #38192

aio/tools/examples/shared/boilerplate/cli-ajs/package.json

@@ -1,6 +1,7 @@
 {
   "name": "angular.io-example",
   "version": "0.0.0",
+  "description": "Example project from an angular.io guide.",
   "license": "MIT",
   "scripts": {
     "ng": "ng",