Fixes functions to use variables set by filter runs (#7906)

* fix: functions should use variables set by filter runs

* refactor: code clean up

* chore: added more tests

editions/test/tiddlers/tests/data/functions/FunctionFilterrunVariables.tid

@@ -0,0 +1,24 @@
+title: Functions/FunctionFilterrunVariables
+description: Functions in filter runs that set variables
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Idiosyncrasy
+caption: Idiosyncrasy Caption Field
+
++
+title: Output
+
+\whitespace trim
+\procedure demo-subfilter() [<currentTiddler>]
+\function .demo-function() [<currentTiddler>]
+
+<$let currentTiddler="Idiosyncrasy">
+<$text text={{{ [<currentTiddler>get[caption]!is[blank]else<currentTiddler>] :map[subfilter<demo-subfilter>] }}}/>,
+<$text text={{{ [<currentTiddler>get[caption]!is[blank]else<currentTiddler>] :map[.demo-function[]] }}}/>
+</$let>
+
++
+title: ExpectedResult
+
+<p>Idiosyncrasy Caption Field,Idiosyncrasy Caption Field</p>

editions/test/tiddlers/tests/data/functions/FunctionFilterrunVariables2.tid

@@ -0,0 +1,20 @@
+title: Functions/FunctionFilterrunVariables2
+description: Functions in filter runs that set variables
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Apple
+cost: 5
+
++
+title: Output
+
+\whitespace trim
+\function .doublecost() [<currentTiddler>get[cost]multiply[2]]
+
+<$text text={{{ [[Apple]] :map[.doublecost[]] }}}/>
+
++
+title: ExpectedResult
+
+10