Add `check__in_string_imports`

[bvssvni]

Sometimes it is nice to use Dyon scripts to analyze Dyon code. The lifetime/type checker has a lot of useful knowledge about the source that currently is not available for Dyon scripts.

For example:

• which functions are called
• from where functions are called
• the type of an expression in the code
• the parent/child relationships of expressions
• the kind of an expression (call, call argument, loop etc.)

By adding a check__in_string_imports, scripts can access the knowledge that the lifetime/type checker has about the source at the end of inference.