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

### **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

Search the React and React Native package READMEs, docs/MDX, Storybook stories, examples, icon gallery pages, and CHANGELOGs for user-facing “Maskicons” references and exported identifiers. Verify the visible name is “Polycons,” add compatibility deprecations and migration notes where needed, then run CI and confirm the example apps compile and render.

Written by the indexing model from the issue text.