{{else}} should render a value rather than be a control-flow keyword.

One thing I noticed as I am both going through the [Svelte tutorial](https://svelte.dev/tutorial/else-blocks) again as well as writing a similar one for Ember / ``, is that `{{else}}` is is syntactically incoherent.

Everywhere else, we use `{{ identifier }}` to render a value _except_ for `{{else}}`.

For consistency, I think we should fix that.
Svelte uses a "continuation" syntax to denote that a block is continuing.

So for us, that would look like this:
```hbs
{{#if condition}}

{{:else if otherCondition}}

{{:else}}

{{/if}}
```
which has 0 ambiguity with value-rendering.