Allow all template literals in non-const positions for slow types

This always results in a `string` type in non `const` positions, so we can always allow it.

We can choose to either leave it or emit a string type. TBD.

```
export let = `asd ${"asd"}`;
```

Start by locating deno_graph's handling of template literals and non-const positions, then reproduce the example from the issue. Clarify whether these literals should be left unchanged or emitted as a string type, and consider the work complete when the chosen behavior is implemented and the example is handled consistently.

Written by the indexing model from the issue text.