Invalid addon metadata causes spurious warning

[ef4]

This library contains two in-repo addons that are intended to support its development. They don't ship in the published npm package. But the package.json file refers to both of them even in the published case.

This means that if you try to build an ember app that has a transitive dependency on simple-html-tokenizer, you get a spurious warning:

WARNING:
WARNING: /Users/edward/hacking/css-blocks/node_modules/simple-html-tokenizer/commands:
WARNING:    Missing package directory

(Normally ember apps don't depend on simple-html-tokenizer because it's consumed as a build step when publishing glimmer-vm, but this is coming up for css-blocks because its glimmer template analyzer uses simple-html-tokenizer.)

[rwjblue]

Unfortunately, there isn't an easy way to have "dev deps" via ember-addon paths. ember-engines has a similar issue and works around it via:

• adding these as dev deps with file: relative paths
• a prepublish script to symlink those into node_modules (otherwise local development sucks since npm/yarn "vendor" them into node_modules and changes aren't live)

I think these should work here too...