Conditional Shortcut Syntax (#7710)

* Initial Commit

* Update docs

* Add support for elseif blocks

* Another test

* WIP

* Change from `{%if%}` to `<%if%>`

See discussion here - https://talk.tiddlywiki.org/t/proposed-if-widget/7882/64

* Don't use the widget body as the template if a list-empty widget is present

See discussion here - https://github.com/Jermolene/TiddlyWiki5/pull/7710#issuecomment-1717193296

* List widget should search recursively for list-template and list-empty

* Allow block mode content within an if/then/else clause

* Update docs

* Add from-version tag to docs

editions/test/tiddlers/tests/data/conditionals/BlockMode.tid

@@ -0,0 +1,37 @@
+title: Conditionals/BlockMode
+description: Basic conditional shortcut syntax in block mode
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Output
+
+\procedure test(animal)
+<% if [<animal>match[Elephant]] %>
+
+! It is an elephant
+
+<% else %>
+
+<% if [<animal>match[Giraffe]] %>
+
+! It is a giraffe
+
+<% else %>
+
+! It is completely unknown
+
+<% endif %>
+
+<% endif %>
+
+\end
+
+<<test "Giraffe">>
+
+<<test "Elephant">>
+
+<<test "Antelope">>
++
+title: ExpectedResult
+
+<h1 class="">It is a giraffe</h1><h1 class="">It is an elephant</h1><h1 class="">It is completely unknown</h1>