[[ RefactorSyntax ]] MCFilter:exec updated
Merged branches refactor-syntax_unicode_shims

Conflicts:
    engine/src/exec.h
    engine/src/exec.cpp
[[ RefactorSyntax ]] MCImport::exec updated
[[ RefactorSyntax ]] EvalOptionalExprAsStringRef updated to EvalOptionalExprAsNullableStringRef when needed