Adds Text substitution support in widget attributes and new operator (#7526)

* feat: new text substitution support, first pass

* fix: use the widget method instead of evaluating a filter

* revert to earlier implementation that emulates macro syntax

* fix: capitalize comments

* feat: add support for triple backticks for substituted attributes

* docs: added docs for substitute operator

* chore: more docs tweaks

* docs: substituted attributes, refactored docs for widget attributes

* docs: fixed typo

* docs: more examples for substituted attributes

* docs: updated prior documentation on concatenating text and variables

* docs: documentation corrections

* Update editions/tw5.com/tiddlers/filters/examples/substitute Operator (Examples).tid

Co-authored-by: btheado <brian.theado@gmail.com>

---------

Co-authored-by: btheado <brian.theado@gmail.com>

editions/test/tiddlers/tests/data/filters/substitute.tid

@@ -0,0 +1,40 @@
+title: Filters/substitute
+description: Test substitute operator
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: substitute filter data 1
+tags: Hello There [[Welcome to TiddlyWiki]] GettingStarted
+
+TiddlyWiki
++
+title: substitute filter data 2
+
+The output of the filter `[[substitute filter data 1]tags[]]` is ${[[substitute filter data 1]tags[]]}$.
++
+title: substitute filter data 3
+
+Welcome to $(projectname)$ $1$ $2$ $3$. Tiddlers starting with `substitute`: ${[prefix[substitute]format:titlelist[]join[ ]]}$.
++
+title: Output
+
+\whitespace trim
+<$let projectname="TiddlyWiki">
+(<$text text={{{ [[]substitute[]] }}}/>)
+(<$text text={{{ [[Hello There, welcome to $TiddlyWiki$]substitute[]] }}}/>)
+(<$text text={{{ [[Welcome to $(projectname)$]substitute[]] }}}/>)
+(<$text text={{{ [[Welcome to $(projectname)$ $1$]substitute[today]] }}}/>)
+(<$text text={{{ [[This is not a valid embedded filter ${ hello )$]substitute[]] }}}/>)
+(<$text text={{{ [{substitute filter data 2}substitute[]] }}}/>)
+(<$text text={{{ [{substitute filter data 3}substitute[every],[day]] }}}/>)
+</$let>
++
+title: ExpectedResult
+
+<p>()
+(Hello There, welcome to $TiddlyWiki$)
+(Welcome to TiddlyWiki)
+(Welcome to TiddlyWiki today)
+(This is not a valid embedded filter ${ hello )$)
+(The output of the filter `[[substitute filter data 1]tags[]]` is Hello.)
+(Welcome to TiddlyWiki every day $3$. Tiddlers starting with `substitute`: [[substitute filter data 1]] [[substitute filter data 2]] [[substitute filter data 3]].)</p>

editions/test/tiddlers/tests/data/widgets/SubstitutedAttributes.tid

@@ -0,0 +1,19 @@
+title: Widgets/SubstitutedAttributes
+description: Attributes specified as string that should have substitution performed.
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Output
+
+\whitespace trim
+<$let project="TiddlyWiki" disabled="true">
+<div class=`$(project)$ 
+${ [[Hello]addsuffix[There]] }$` attrib=`myvalue` otherattrib=`$(1)$` blankattrib=`` quoted="here" disabled=```$(disabled)$```>
+</div>
+</$let>
+
++
+title: ExpectedResult
+
+<p><div attrib="myvalue" blankattrib="" class="TiddlyWiki 
+HelloThere" disabled="true" otherattrib="" quoted="here"></div></p>