refactor: When Vue SFCs are source files, make them as layout components directly.

Author: ulivz

packages/@vuepress/core/lib/internal-plugins/routes.js

@@ -16,11 +16,12 @@ function importCode () {
   return `
 import { injectComponentOption } from '@app/util'
 import rootMixins from '@internal/root-mixins'
-import components from '@internal/layout-components'
+import layoutComponents from '@internal/layout-components'
+import pageComponents from '@internal/page-components'
 import LayoutDistributor from '@app/components/LayoutDistributor.vue'
 
 injectComponentOption(LayoutDistributor, 'mixins', rootMixins)
-injectComponentOption(LayoutDistributor, 'components', components)
+injectComponentOption(LayoutDistributor, 'components', Object.assign({}, layoutComponents, pageComponents))
 `
 }
 

packages/@vuepress/core/lib/prepare/Page.js

@@ -123,7 +123,10 @@ module.exports = class Page {
         }
       } else if (this._filePath.endsWith('.vue')) {
         const { data = {}} = parseVueFrontmatter(this._content)
-        this.frontmatter = data
+        // When Vue SFCs are source files, make them as layout components directly.
+        this.frontmatter = Object.assign({
+          layout: this.key
+        }, data)
       }
     }