feat(height, width): update to SHINE sizing

[dancormier]

SPARK-154

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This PR updates our set of "sizing units" to the new batch detailed in SPARK-154. I also took this opportunity to clean up our sizing/spacing in general to make it easier to maintain.

Notable changes

Visual

Docs

• Split width-height.html into width.html and height.html
  • I felt the single page was too difficult to traverse and too noisy.

Under the hood

• Consolidated two #build-classes Less functions into a single one
• Split width-height.less into width.less and height.less

Custom properties

• Replaced property calcs of negative values
  • For example, calc(var(--su1) * -1)) becomes var(--sun1)
  • These changes represent the majority or .less files changed
• Replaced any references to --s-full and --s-step with their sizing unit counterparts
  • For example, calc(var(--s-step) * 10) becomes --su1024

Tests

• Updated Less snapshot tests for "spacing" (aka margin and padding)
• Added Less snapshot tests for height, positioning, sizing, and width

How to test

TODO

• Complete docs
• Add less tests
• Add changeset
• Complete Migration Guide updates

[changeset-bot]

🦋 Changeset detected

Latest commit: 1278bf9

The changes in this PR will be included in the next version bump.

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