Port component-reading-position repo into this monorepo

[jeffpaul]

Is your feature request related to a problem? Please describe.
Baseline references Reading Position (see https://baseline.10up.com/component/reading-position/), but links out to https://github.com/10up/component-reading-position instead of a sub-package in this repo.

Describe the solution you'd like

• port https://github.com/10up/component-reading-position into https://github.com/10up/component-library
• update https://baseline.10up.com/component/reading-position/ links to monorepo
• add component-reading-position label
• archive https://github.com/10up/component-reading-position

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.