fix: Move content into to frontend directory

Doing this BEFORE the merge prevents a lot of merge conflicts.

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

frontend/src/components/markdown-renderer/hooks/use-configured-markdown-it.ts

@@ -0,0 +1,35 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { useMemo } from 'react'
+import MarkdownIt from 'markdown-it/lib'
+import type { MarkdownRendererExtension } from '../extensions/base/markdown-renderer-extension'
+
+/**
+ * Creates a new {@link MarkdownIt markdown-it instance} and configures it using the given {@link MarkdownRendererExtension markdown renderer extensions}.
+ *
+ * @param extensions The extensions that configure the new markdown-it instance
+ * @param allowHtml Defines if html in markdown is allowed
+ * @param newlinesAreBreaks Defines if new lines should be treated as line breaks or paragraphs
+ * @return the created markdown-it instance
+ */
+export const useConfiguredMarkdownIt = (
+  extensions: MarkdownRendererExtension[],
+  allowHtml: boolean,
+  newlinesAreBreaks: boolean
+): MarkdownIt => {
+  return useMemo(() => {
+    const newMarkdownIt = new MarkdownIt('default', {
+      html: allowHtml,
+      breaks: newlinesAreBreaks,
+      langPrefix: '',
+      typographer: true
+    })
+    extensions.forEach((extension) => newMarkdownIt.use((markdownIt) => extension.configureMarkdownIt(markdownIt)))
+    extensions.forEach((extension) => newMarkdownIt.use((markdownIt) => extension.configureMarkdownItPost(markdownIt)))
+    return newMarkdownIt
+  }, [allowHtml, extensions, newlinesAreBreaks])
+}