Reloader and pin_all_from not picking up assets transformed by the asset pipeline

[mtgrosser]

Currently, importmaps don't work properly with JS assets which have their filename extension transformed by the Rails asset pipeline from something other than .js to .js:

• pin_all_from only matches .js(m) files
• The cache sweeper file watcher only watches for .js files

Use cases for other filename extensions include:

• the default Sprockets functionality of transforming .js.erb to .js
• transformations for framework-specific file formats like .vue and .jsx

For example, we are using the jass-vue-sfc gem to transform .vue components into ES modules, which are then loaded by import maps. The same can be achieved for JSX files with jass-react-jsx.

In PR #57 I'm proposing adding config.importmap.accept which would allow importmaps to pin other filename extensions than .js, while staying agnostic to the asset pipeline used.