KaTeX - EditorToolbar stamp button for wysiwyg katex snippet input (#3131)

* add KaTeX logo

* add katex stamp button

* add katex stamp dropdown

* add a snippet so that the dropdown isn't empty

* correct dropdown title

* change tag

* update snippets tag

plugins/tiddlywiki/katex/katex-logo.tid

@@ -0,0 +1,3 @@
+title: $:/plugins/tiddlywiki/katex/katex-logo
+
+$$\KaTeX$$

plugins/tiddlywiki/katex/snippets/logo.tid

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+title: $:/plugins/tiddlywiki/katex/snippets/logo
+tags: $:/tags/KaTeX/Snippet
+
+$$\KaTeX$$

plugins/tiddlywiki/katex/ui/EditorToolbar/katex-dropdown.tid

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+title: $:/plugins/tiddlywiki/katex/ui/EditorToolbar/katex-dropdown
+
+\define toolbar-button-stamp-inner()
+<$button tag="a">
+
+<$action-sendmessage
+	$message="tm-edit-text-operation"
+	$param="replace-selection"
+	text={{$(snippetTitle)$}}
+/>
+
+<$action-deletetiddler
+	$tiddler=<<dropdown-state>>
+/>
+
+<$view tiddler=<<snippetTitle>> field="caption" mode="inline">
+
+<$transclude tiddler=<<snippetTitle>> mode="inline"/>
+
+</$view>
+
+</$button>
+\end
+
+<$list filter="[all[shadows+tiddlers]tag[$:/tags/KaTeX/Snippet]!has[draft.of]sort[caption]]" variable="snippetTitle">
+
+<<toolbar-button-stamp-inner>>
+
+</$list>
+
+----
+
+<$button tag="a">
+
+<$action-sendmessage
+	$message="tm-new-tiddler"
+	tags="$:/tags/KaTeX/Snippet"
+	text="""$$snippet$$"""
+/>
+
+<$action-deletetiddler
+	$tiddler=<<dropdown-state>>
+/>
+
+<em>
+
+<$text text={{$:/language/Buttons/Stamp/Caption/New}}/>
+
+</em>
+
+</$button>
+
+[ext[KaTeX functions catalogue|https://khan.github.io/KaTeX/function-support.html]]

plugins/tiddlywiki/katex/ui/EditorToolbar/katex.tid

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+title: $:/plugins/tiddlywiki/katex/ui/EditorToolbar/katex
+tags: $:/tags/EditorToolbar
+icon: $:/plugins/tiddlywiki/katex/katex-logo
+caption: katex
+description: create and insert preconfigured KaTeX snippets
+condition: [<targetTiddler>!is[image]]
+dropdown: $:/plugins/tiddlywiki/katex/ui/EditorToolbar/katex-dropdown
+text: