feat: add feature plugin tests and validation for feature flags

vite-layers/test/fixtures/devtools/base/app.config.ts

@@ -0,0 +1,7 @@
+export default {
+  name: 'base',
+  features: { billing: true, shared: 'base', nested: { on: true } },
+  hooks: {
+    'layers:resolved': () => {},
+  },
+}

vite-layers/test/fixtures/devtools/base/public/favicon.svg

@@ -0,0 +1 @@
+<svg><!-- base favicon --></svg>

vite-layers/test/fixtures/devtools/base/public/logo.svg

@@ -0,0 +1 @@
+<svg><!-- base logo --></svg>

vite-layers/test/fixtures/devtools/base/src/components/Footer.vue

@@ -0,0 +1 @@
+<template><footer>base footer</footer></template>

vite-layers/test/fixtures/devtools/base/src/components/Header.vue

@@ -0,0 +1 @@
+<template><header>base header</header></template>

vite-layers/test/fixtures/devtools/base/src/pages/Billing.vue

@@ -0,0 +1 @@
+<template><div>billing</div></template>