[ALOY-1236] Binding notation should allow mixed variables and plain text

Alloy's databinding syntax lets you mix binding selectors and plain text in some ways, but not others. What is permitted and what is not supported is not obvious or intuitive. Binding should simply replace the variable wherever it is present.

<Label id="foo" text="This should {work}"/>
<Label id="foo" text="{work} this should"/>
<Label id="foo" text="{workstoo}"/>
<Label id="foo" text="{model.get} {model.to} {model.work}"/>

Some complex binding was enabled through ALOY-443, but not all combinations. Relates to https://github.com/EtnaTraining/MoviesDemo/issues/2