Add support for JSON-formatted tiddler store, and make it the default (#5708)

* Add support for JSON-formatted tiddler store, and make it the default

The change to `getTiddlersAsJson()` is to allow experimentation

* Move JSON tiddlers into their own store area, and fix support for encrypted tiddlers

Also add a dummy old-style store area for backwards compatibility

The current arrangement is that JSON tiddlers will always override old-style tiddlers.

* Use the deserialiser mechanism to decode the content

* Refactor $:/core/modules/deserializers.js before we start extending it

Cleaning up the helper function names and ordering

* Drop support for the "systemArea" div

It was only used in really old v5.0.x

* Update deserializer to support JSON store format and add some tests

* Life UI restrictions on characters in fieldnames

* Add another test case

* Correct mis-merge

* Remove toLowerCase() methods applied to fieldnames

* Insert line breaks in output of getTiddlersAsJson (#5786)

Rather than have the entire store on one line, insert a line break
after each tiddler.

* Refactor #5786 for backwards compatibility

* Only read .tiddlywiki-tiddler-store blocks from script tags

Prompted by @simonbaird's comment here: https://github.com/Jermolene/TiddlyWiki5/pull/5708#discussion_r648833367

* Clean up escaping of unsafe script characters

It seems that escaping `<` is sufficient

* Add docs from @saqimtiaz

Thanks @saqimtiaz

* Docs tweaks

* Remove excess whitespace

Thanks @simonbaird

* Fix templates for lazy loading

* Remove obsolete item from release note

* Clean up whitespace

* Docs for the jsontiddler widget

* Fix whitespace

Fixes #5840

* Comments

* Fix newlines in JSON store area

* Remove obsolete docs change

Co-authored-by: Simon Baird <simon.baird@gmail.com>

languages/zh-Hans/Misc.multids

@@ -41,7 +41,6 @@ Error/WhileSaving: 保存时，发生错误
 Error/XMLHttpRequest: XMLHttpRequest 错误代码
 InternalJavaScriptError/Title: 内部的 JavaScript 错误
 InternalJavaScriptError/Hint: 喔，真是令人尴尬。建议刷新您的浏览器，重新启动 TiddlyWiki
-InvalidFieldName: 字段名称 "<$text text=<<fieldName>>/>" 包含无效字符，字段名称只能包含小写字母、数字、底线 (`_`)、 连字号 (`-`) 和小数点 (`.`)
 LayoutSwitcher/Description: 打开布局切换器
 LazyLoadingWarning: <p>正在从 ''<$text text={{!!_canonical_uri}}/>'' 加载外部内容 ...</p><p>如果此信息未消失，可能是条目内容类型与外部内容的类型不匹配，或是您可能正在使用的浏览器，不支援单文件式维基的外部内容。请参阅 https://tiddlywiki.com/#ExternalText</p>
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