This change accomplishes several tasks towards unifying our JavaScript

build infrastructure and supported more modern node.js environments:

Replace many specific dependencies with a new dependency on

@beanbag/js-buildkit.
Eliminate unused or obsolete dependencies.
Base tsconfig.json on our shared config.
Copy our customized @types/backbone into this source tree, rather

  than referencing it from node_modules. I'm working on upstreaming

  these changes so we don't have to ship our own at all.
Ship types as both index.d.ts and index.d.mts.
Update to ESLint 9.

Plus a few changes relating to fixing unit tests:

Use @babel/register for transpiling during jasmine testing rather

  than ts-node. It seems like the ts-node one was broken on modern

  node environments, and using babel instead keeps our unit tests

  running in a much closer mode to how the code is built for packaging.

  This required some massaging of our babel configuration to allow

  slightly different plugin configurations between dev and test.
Import MenuItemsRadioGroup as type MenuItemsRadioGroup in

  menuItemModel.ts in order to prevent a circular dependency.
Use this.constructor for static member access inside MenuView, so

  unit tests and the class itself aren't looking at different versions

  of static members.

Did a build.
Ran unit tests.
Ran storybook.
Used this is a workspace with other packages that depend on it.