fix(v2): Fix MDX docs being considered as partials when siteDir match the _ prefix convention (#5199)

* Add _ to dogfood docs folder to cover against edge case

* Fix edge case with MDX partials when site / content dir contains a _ prefix

* add globUtils tests

* proper dogfooding folder re-organization, all content plugins being used

* refactor dogfooding folder + expose /tests page index

* fix page plugin ignoring options.routeBasePath

packages/docusaurus-plugin-content-docs/src/index.ts

@@ -18,7 +18,7 @@ import {
   reportMessage,
   posixPath,
   addTrailingPathSeparator,
-  createMatcher,
+  createAbsoluteFilePathMatcher,
 } from '@docusaurus/utils';
 import {LoadContext, Plugin, RouteConfig} from '@docusaurus/types';
 import {loadSidebars, createSidebarsUtils, processSidebars} from './sidebars';
@@ -394,9 +394,10 @@ export default function pluginContentDocs(
       };
 
       function createMDXLoaderRule(): RuleSetRule {
+        const contentDirs = flatten(versionsMetadata.map(getDocsDirPaths));
         return {
           test: /(\.mdx?)$/,
-          include: flatten(versionsMetadata.map(getDocsDirPaths))
+          include: contentDirs
             // Trailing slash is important, see https://github.com/facebook/docusaurus/pull/3970
             .map(addTrailingPathSeparator),
           use: compact([
@@ -409,7 +410,10 @@ export default function pluginContentDocs(
                 beforeDefaultRehypePlugins,
                 beforeDefaultRemarkPlugins,
                 staticDir: path.join(siteDir, STATIC_DIR_NAME),
-                isMDXPartial: createMatcher(options.exclude),
+                isMDXPartial: createAbsoluteFilePathMatcher(
+                  options.exclude,
+                  contentDirs,
+                ),
                 metadataPath: (mdxPath: string) => {
                   // Note that metadataPath must be the same/in-sync as
                   // the path from createData for each MDX.