* feat(icons): add square-text
Adds square-text: a solid square containing three ragged lines of text.
The set has square-dashed-text but no solid-border equivalent, which is
the same asymmetry solid/dashed pairs elsewhere avoid. This reuses
square-dashed-text's exact text glyph (M7 8h8 / M7 12h10 / M7 16h6) on the
standard 18x18 rx=2 square, so it reads as the solid twin.
Distinct from square-menu, whose lines are equal full-width (a menu, not
running text).
* chore(icons): expand square-text tags and fill use-cases
Applies the metadata bot's tag suggestions (curated) and fills the
use-cases field.
* chore(icons): promote lab/text-square to square-text
Per review on #4609: square-text is identical to lab/text-square, so
this removes the lab entry and merges its metadata (tags + development
category) into the promoted icon.
* chore(icons): credit danielbayley and expand square-text use-cases
Per review on #4609: adds @danielbayley (original author of lab/text-square)
to contributors, and expands use-cases per @ericfennis.
