Support logical operators in HTML Template code

I often have much redundancy when just trying to pass conditional paramters. For example:

```html
{{#if condition}}
{{> otherTemplate param=1}}
{{else}}
{{> otherTemplate param=2}}
{{/if}}
```

alternative would be now to create another helper (because `condition` is shared, which I can't simply return the value from this helpert) but that increases the js code a lot for many simple conditions.

Way better would be

```html
{{> otherTemplate param=(condition ? 1 : 2)}}
```

That would also make many custom Template helpers packages obsolete and thus again reduce bundle size.

Any ideas or ciritcs on that?

The payload names no files or tests. Start by reviewing the conditional-template examples and linked pull request #500 to understand the proposed syntax and current status; done should mean a defined logical-operator form supports the shown conditional parameter without an extra helper.

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