Rename “Maskicons” to “Polycons” in React and React Native libraries

[georgewrmarshall]

Description

Per internal thread, “Maskicons” is being renamed to “Polycons.” Update all user‑facing references across the design system’s React and React Native packages, docs, Storybook, and examples.

Technical Details

• Replace user‑facing text “Maskicons” → “Polycons” in READMEs, docs/MDX, Storybook stories, and examples.
• Update Storybook titles/descriptions and any icon gallery pages.
• If exported identifiers contain “Maskicons”, add “Polycons” equivalents and deprecate the old names (no removal in this issue).
• Add CHANGELOG entry and brief migration notes.

Acceptance Criteria

• All visible references show “Polycons” in React and React Native packages.
• Storybook/docs reflect the new name.
• No breaking API changes; deprecations added if needed.
• CI passes; no TS/lint violations.
• Example apps still compile and render correctly.

References

• Slack: https://consensys.slack.com/archives/C080KDTTF6Y/p1757961587668139?thread_ts=1747678228.607619&cid=C080KDTTF6Y