E2E test harness for Vue 3

"Yarn workspaces" uses its understanding of the build graph in a limited way, so to recompile and run just this set of E2E tests, you can run these commands at the project root:

yarn workspace @builder.io/e2e-app run build
yarn workspace @builder.io/e2e-vue3 run build
yarn workspace @builder.io/e2e-vue3 run e2e

This test harness copies the source output from the e2e-app project, because that project emits Vue source code, rather than the compiled format suitable for consumption via node_modules. While it is surely possible to consume .vue files from node_modules, that isn't idiomatic and simple attempt yield partially-broken components.