Template helper function improvements

[toasted-nutbread]

Fixes #437. Was due to the different modalities that helpers can be used in:

The following would work:

{{~#*inline "test"~}}
    {{~#scope~}}
        {{~#regexMatch "test" "gu"~}}test{{~/regexMatch~}}
    {{~/scope~}}
{{~/inline~}}
{{~> (lookup . "marker") ~}}

The following would not work:

{{~#*inline "test"~}}
    {{~#scope~}}
        {{~set "value" (regexMatch "test" "gu" "test")}}
    {{~/scope~}}
{{~/inline~}}
{{~> (lookup . "marker") ~}}

[github-actions]

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