analyses: add global alias analysis

[ekiwi]

I will write tests over the next couple of weeks/months.

Contributor Checklist

• [ ] Did you add Scaladoc to every public function/method?
• [ ] Did you update the FIRRTL spec to include every new feature/behavior?
• [ ] Did you add at least one test demonstrating the PR?
• [ ] Did you delete any extraneous printlns/debugging code?
• [ ] Did you specify the type of improvement?
• [ ] Did you state the API impact?
• [ ] Did you specify the code generation impact?
• [ ] Did you request a desired merge strategy?
• [ ] Did you add text to be included in the Release Notes for this change?

Type of Improvement

• new feature/API

API Impact

• adds an AliasAnlysis object

Backend Code Generation Impact

• none

Desired Merge Strategy

• squash

Release Notes

Reviewer Checklist (only modified by reviewer)

• [ ] Did you add the appropriate labels?
• [ ] Did you mark the proper milestone (1.2.x, 1.3.0, 1.4.0) ?
• [ ] Did you review?
• [ ] Did you check whether all relevant Contributor checkboxes have been checked?
• [ ] Did you mark as Please Merge?