ZIP Exports: Finished up format doc, move files, started builder

Moved all existing export related app files into their new own dir.

app/Exports/Controllers/PageExportController.php

@@ -0,0 +1,77 @@
+<?php
+
+namespace BookStack\Exports\Controllers;
+
+use BookStack\Entities\Queries\PageQueries;
+use BookStack\Entities\Tools\PageContent;
+use BookStack\Exceptions\NotFoundException;
+use BookStack\Exports\ExportFormatter;
+use BookStack\Http\Controller;
+use Throwable;
+
+class PageExportController extends Controller
+{
+    public function __construct(
+        protected PageQueries $queries,
+        protected ExportFormatter $exportFormatter,
+    ) {
+        $this->middleware('can:content-export');
+    }
+
+    /**
+     * Exports a page to a PDF.
+     * https://github.com/barryvdh/laravel-dompdf.
+     *
+     * @throws NotFoundException
+     * @throws Throwable
+     */
+    public function pdf(string $bookSlug, string $pageSlug)
+    {
+        $page = $this->queries->findVisibleBySlugsOrFail($bookSlug, $pageSlug);
+        $page->html = (new PageContent($page))->render();
+        $pdfContent = $this->exportFormatter->pageToPdf($page);
+
+        return $this->download()->directly($pdfContent, $pageSlug . '.pdf');
+    }
+
+    /**
+     * Export a page to a self-contained HTML file.
+     *
+     * @throws NotFoundException
+     * @throws Throwable
+     */
+    public function html(string $bookSlug, string $pageSlug)
+    {
+        $page = $this->queries->findVisibleBySlugsOrFail($bookSlug, $pageSlug);
+        $page->html = (new PageContent($page))->render();
+        $containedHtml = $this->exportFormatter->pageToContainedHtml($page);
+
+        return $this->download()->directly($containedHtml, $pageSlug . '.html');
+    }
+
+    /**
+     * Export a page to a simple plaintext .txt file.
+     *
+     * @throws NotFoundException
+     */
+    public function plainText(string $bookSlug, string $pageSlug)
+    {
+        $page = $this->queries->findVisibleBySlugsOrFail($bookSlug, $pageSlug);
+        $pageText = $this->exportFormatter->pageToPlainText($page);
+
+        return $this->download()->directly($pageText, $pageSlug . '.txt');
+    }
+
+    /**
+     * Export a page to a simple markdown .md file.
+     *
+     * @throws NotFoundException
+     */
+    public function markdown(string $bookSlug, string $pageSlug)
+    {
+        $page = $this->queries->findVisibleBySlugsOrFail($bookSlug, $pageSlug);
+        $pageText = $this->exportFormatter->pageToMarkdown($page);
+
+        return $this->download()->directly($pageText, $pageSlug . '.md');
+    }
+}