Make asUInt on Bundle Literals work outside of Builder context

[KasperHesse]

Type of issue: feature request

Impact: | API modification

Development Phase: request

Other information

When calling asUInt() on a bundle literal outside of a builder context, it currently raises a ChiselException: Error: Not in UserModule. Being able to call asUInt() on bundle literals outside the Builder context (eg in a tester) would make testing easier. See https://gitter.im/freechipsproject/chisel3?at=605469f03a9448256c1703a for an example of the code that raises this exception.

If the current behavior is a bug, please provide the steps to reproduce the problem:
N/A

What is the current behavior?
It raises a chisel3.internal.ChiselException

What is the expected behavior?
It should cast the bundle to a UInt representing the same bit values.

Please tell us about your environment:

Chisel version: 3.4.2
OS: Windows 10, build 19042.867 running openJDK 11.0.8
What is the use case for changing the behavior?
Casting to/from bundle literals and UInts seems like a useful feature to have outside of Builders.

[jackkoenig]

This is related to the DataView work I'm doing so I will try to fix this as part of that.