YAML headers, special symbols and table broken => RAW MODE suggested

[robert-winkler]

YAML headers and special symbols modified on reading/writing
For adding document information in markdown documents, YAML headers are common. Those are changed when the markdown files are edited with Text. As well, I noticed the undesired 'optimization' of text, such as [] is changed to [ ], and \delta becomes \delta. Additionally, a pipe table becomes modified in my document. This behavior breaks things, e.g., when processing the MD file with Pandoc (https://pandoc.org/, https://peerj.com/articles/cs-112/).

Expected behavior
Existing markdown code/text should be left unmodified.

Reproduce - YAML

1. Create a markdown file with a YAML header

---
title: The life of Donald
author: Donald Duck
---

2. Upload and modify the file in Nextcloud/Text
3. Download and compare

Reproduce - Symbols/ Commands

1. Create a markdown file with special symbols

[@markof_et_al_2019]
$\delta$

2. Upload and modify the file in Nextcloud/Text
3. Download and compare

Reproduce - Table

1. Create a markdown file with a pipe table

| Hello | World |
| ------- | -------- |
| Mick  | 2017   |

2. Upload and modify the file in Nextcloud/Text
3. Download and compare

SUGGESTION
Provide a RAW MODE option (similar to the previous Markdown Nextcloud editor).

[nilsbecker]

This appears to be a duplicate of #772