Refactor BitSet implementation with unittest and doc

[OceanS2000]

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?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
• 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

• documentation
• code refactoring

API Impact

This PR adds several operations for manipulation of more generic bit pattern (BitSetFamily) and generate a matching decoder from such a (probably complex) pattern with decoder API.

The API should be backward compatible with existing code using BitPat

Backend Code Generation Impact

Desired Merge Strategy

Release Notes

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels?
• 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)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you mark as Please Merge?