Preserve literals across .asUInt

[jackkoenig]

Also working on supporting preserving literals across .asTypeOf, but this is the first step.

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
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Type of Improvement

• Feature (or new API)

Desired Merge Strategy

• Squash

Release Notes

This is mostly useful for initial values for async reset registers and for constructing literal values in testing contexts (e.g. ChiselSim). It also should slightly reduce memory use and .fir size.

Reviewer Checklist (only modified by reviewer)

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• Did you do one of the following when ready to merge:
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[seldridge]

The code change looks correct to me. This is a nice improvement.

The tests are quite verbose. I don't have a good suggestion on how to get them smaller, though.

[jackkoenig]

The tests are quite verbose. I don't have a good suggestion on how to get them smaller, though.

Yeah me neither, especially because I think it is important to check weird Bundle Literals