Refresh Approximation units (aka "Whimsical" units)

Problem Statement In general, we want to provide "real world" approximations for conversions to help users conceptually grasp the magnitude of the values being displayed while performing unit conversions. However, we do not currently scale these approximations or document them as well as we should.

Evidence or User Insights The community has identified gaps in our documentation in regards to these units (#120). There is also some confusion around when we decide to show which units (#335).

Proposal Improve the approximation units we display and how we display them by defining an appropriate scaled set of approximations for each applicable unit converter type and auditing the set of units we display today for accuracy. We should also more thoroughly documenting these units.

Goals

• Present representative approximations across all applicable unit converters
• Approximations are accurate and scale appropriately with magnitude of inputted values (e.g., maybe we should add "Olympic size swimming pool" for really large volumes)

Non-Goals

• None

Low-Fidelity Concept N/A (we should leverage the existing design).