* @grafana/toolkit: make ts-loader ignore files that are not bundled

* @grafana/toolkit: improve the circleci task (#18133)

This PR makes some minor improvements to the circle task

Adds build info to plugin.json
adds dependencies to deployed artifacts
Makes sure prettier has content before writing (avoid writing empty files)
renames 'bundle' to 'package' and saves stuff in a 'packages' file

* @grafana/toolkit: enable plugin themes to work with common stylesheet (#18160)

This makes it possible to use themes styleshheet files and stylesheet imports at the same time. The problem occurred when trying to migrate polystat panel to toolkit: grafana/grafana-polystat-panel#62