Implement module prefix API

[jared-barocsi]

Contributor Checklist

• [x] Did you add Scaladoc to every public function/method?
• [x] Did you add at least one test demonstrating the PR?
• [x] Did you delete any extraneous printlns/debugging code?
• [x] Did you specify the type of improvement?
• [ ] Did you add appropriate documentation in docs/src?
• [x] Did you state the API impact?
• [x] Did you specify the code generation impact?
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• [x] Did you add text to be included in the Release Notes for this change?

Type of Improvement

• new feature/API

API Impact

Adds new API

Backend Code Generation Impact

No impact

Desired Merge Strategy

Squash and merge

Release Notes

Implement Module Prefix API

• Adds a new object, withModulePrefix(prefix), that prefixes all instantiated modules within its scope with the prefix argument
• Can be nested either directly in itself, or within modules created in its scope

Reviewer Checklist (only modified by reviewer)

• [x] Did you add the appropriate labels?
• [x] Did you mark the proper milestone (Bug fix: 3.3.x, [small] API extension: 3.4.x, API modification or big change: 3.5.0)?
• [x] Did you review?
• [x] Did you check whether all relevant Contributor checkboxes have been checked?
• [ ] Did you mark as Please Merge?

[mwachs5]

Discussed this again with @jackkoenig . The main limitation of this PR as it is is that we lose the "what is the prefix (ad-hoc namespace)" and "what is the leaf name" distinction. I'd suggest we do one of (in increasing order of complexity / design thought required):

1. make some convention that names can be . - separated into .fir, and lowered later to concatenate these names (minor firrtl spec expansion). Then make this PR use . to separate the prefixes
2. Add a first class concept of "prefix" to firrtl spec and pass the prefix in directly
3. Add a first class concept of "namespace" to firrtl spec and stop using prefix as ad-hoc namespace