Introduce GitHub markdown editor, keep EasyMDE as fallback (#23876)

The first step of the plan

* #23290

Thanks to @silverwind for the first try in #15394 . Close #10729 and a
lot of related issues.

The EasyMDE is not removed, now it works as a fallback, users can switch
between these two editors.

Editor list:

* Issue / PR comment
* Issue / PR comment edit
* Issue / PR comment quote reply
* PR diff view, inline comment
* PR diff view, inline comment edit
* PR diff view, inline comment quote reply
* Release editor
* Wiki editor

Some editors have attached dropzone

Screenshots:

<details>


![image](https://user-images.githubusercontent.com/2114189/229363558-7e44dcd4-fb6d-48a0-92f8-bd12f57bb0a0.png)


![image](https://user-images.githubusercontent.com/2114189/229363566-781489c8-5306-4347-9714-d71af5d5b0b1.png)


![image](https://user-images.githubusercontent.com/2114189/229363771-1717bf5c-0f2a-4fc2-ba84-4f5b2a343a11.png)


![image](https://user-images.githubusercontent.com/2114189/229363793-ad362d0f-a045-47bd-8f9d-05a9a842bb39.png)

</details>

---------

Co-authored-by: silverwind <me@silverwind.io>

templates/repo/wiki/new.tmpl

@@ -19,15 +19,18 @@
 			<div class="help">
 				{{.locale.Tr "repo.wiki.page_name_desc"}}
 			</div>
-			<div class="ui top attached tabular menu previewtabs" data-write="write" data-preview="preview">
-				<a class="active item" data-tab="write">{{.locale.Tr "write"}}</a>
-				<a class="item" data-tab="preview" data-url="{{$.Repository.Link}}/markup" data-context="{{$.RepoLink}}">{{$.locale.Tr "preview"}}</a>
-			</div>
-			<div class="field content" data-loading="{{.locale.Tr "loading"}}">
-				<div class="ui bottom active tab" data-tab="write">
-					<textarea class="js-quick-submit" id="edit_area" name="content" data-id="wiki-{{.title}}" data-url="{{.Repository.Link}}/markup" data-context="{{.RepoLink}}">{{if .PageIsWikiEdit}}{{.content}}{{else}}{{.locale.Tr "repo.wiki.welcome"}}{{end}}</textarea>
-				</div>
-			</div>
+
+			{{$content := .content}}
+			{{if not .PageIsWikiEdit}}
+				{{$content = .locale.Tr "repo.wiki.welcome"}}
+			{{end}}
+			{{template "shared/combomarkdowneditor" (dict
+				"locale" $.locale
+				"MarkdownPreviewUrl" (print .Repository.Link "/markup")
+				"MarkdownPreviewContext" .RepoLink
+				"TextareaName" "content"
+			)}}
+
 			<div class="field">
 				<input name="message" placeholder="{{.locale.Tr "repo.wiki.default_commit_message"}}">
 			</div>