Consider running `eslint` "as-if-foss" to catch potential FOSS-specific failures in advance

In #227004 (closed) we can see that eslint (and assets compilation) can fail in FOSS when a FOSS file includes a line like import HealthStatusSelect from 'ee_else_ce/vue_shared/components/sidebar/health_status_select/health_status_bundle'; but when no app/assets/javascripts/vue_shared/components/sidebar/health_status_select/health_status_bundle file exists.

I believe we could catch these problems in advance by running eslint in a "as-if-foss" fashion.