add component density Tests

[onufer]

Description

• revert renames of applyHotHeightDensityReduction, and applyMaterialMassFracsToNumberDensities from recent PR
  • Justification: the old names are correct enough and we prefer a stable API
• add getMassDensity() function to components
• adding component density/mass tests for expansion
• add test demonstrating that construction of components programmatically isn't the same as through blueprints

---

Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes are up-to-date with any bug fixes or new features.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in setup.py.

[onufer]

We probably want to fix this. it is documented in #819

[onufer]

The fact that we need this is indicative of a bug. Thankfully the differences are very minor.
#820

[john-science]

I love it when people add tests! Reviewing now.

[john-science]

I would be curious to know how this problem relates to this docstring:

armi/armi/materials/material.py

Lines 341 to 348 in bc556fc

	def density(self, Tk: float = None, Tc: float = None) -> float:
	"""
	Return density that preserves mass when thermally expanded in 2D.
	Warning
	-------
	This density will not agree with the component density since this method only expands in 2 dimensions.
	The component has been manually expanded axially with the manually entered block hot height.

This has been in our codebase for at least 3 years.

[onufer]

@john-science, that doc string indicates that until you fix it it will be off by axial expansion factor. but its not exactly off axial expansion factor, and that is the problem.. It should agree exactly with this one, but it doesn't

armi/armi/materials/material.py

Lines 357 to 358 in bc556fc

	armi.materials.density3:
	component density should be in agreement with this density

[john-science]

I love it when people add more tests.

These two kind of "prove a negative", which is unusual. But they are still really helpful to have around.