Resolve #3518198 "Set code component"

Closes #3518198

This MR:

• sets an array of js component depdencies to be sent to the backend under the imported_js_components property. ex. ['my_heading', "my_heading2", "my_button"] (the values are machine names)
• supports previews for imported code components under the '@/components/" scope
• created new error card to display in preview if user tries to import a component that doesn't exist or has no auto-save state
• added unit tests for function that gets import declarations from ast