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/hooks/common/use-trimmed-note-markdown-content-without-frontmatter.ts

@@ -0,0 +1,34 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { useMemo } from 'react'
+import { useApplicationState } from './use-application-state'
+
+/**
+ * Returns the markdown content from the global application state trimmed to the maximal note length and without the frontmatter lines.
+ *
+ * @return The array of markdown content lines
+ */
+export const useTrimmedNoteMarkdownContentWithoutFrontmatter = (): string[] => {
+  const maxLength = useApplicationState((state) => state.config.maxDocumentLength)
+  const markdownContent = useApplicationState((state) => ({
+    lines: state.noteDetails.markdownContent.lines,
+    content: state.noteDetails.markdownContent.plain
+  }))
+  const lineOffset = useApplicationState((state) => state.noteDetails.frontmatterRendererInfo.lineOffset)
+
+  const trimmedLines = useMemo(() => {
+    if (markdownContent.content.length > maxLength) {
+      return markdownContent.content.slice(0, maxLength).split('\n')
+    } else {
+      return markdownContent.lines
+    }
+  }, [markdownContent, maxLength])
+
+  return useMemo(() => {
+    return trimmedLines.slice(lineOffset)
+  }, [lineOffset, trimmedLines])
+}