- Fix #54241
- ### Problem

  The `import` statement generated is incorrect for Rails applications
  using importmap and a css processor.

  ### Context

  Rails applications using `importmap` and having a `package.json`,
  would get a `channel.js` file generated with a relative path,
  whereas the correct import statement needs to match the name of the
  importmap json keys.

  This is because the generator assumes that if a `package.json`
  exists in the project, this means it uses a javascript bundling
  tool. This assumption is not correct as one can be using importmap
  while still having `package.json` for processing css.
  This is the case when you generate your application like this:
  `rails new blorgh --css postcss`

  ### Solution

  Add the right import statement by checking if the project uses
  importmap.