feat: Add watchAsset origin metadata fallbacks

[pedronfigueiredo]

Handle optional origin/pageMeta inputs in watchAsset approvals. Add tests covering empty-string origin fallbacks and requestMetadata precedence.

Explanation

References

Related to https://github.com/MetaMask/mobile-planning/issues/2395

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

---

Note

Enhances watchAsset approval flow with origin/page metadata handling and safer defaults.

• TokensController.watchAsset accepts optional origin, pageMeta, and requestMetadata; origin resolves via getNonEmptyString with fallback to ORIGIN_METAMASK, and pageMeta is forwarded in requestData.metadata
• Extends SuggestedAssetMeta and adds WatchAssetRequestMetadata; imports Json; new getNonEmptyString helper
• Approval request now normalizes empty image to null
• Refactors multiple || to ?? and adds trim checks when defaulting token image URLs
• Tests added for empty-string origin fallback and requestMetadata.origin precedence
• Changelog updated to note watchAsset origin/page metadata support

^{Written by Cursor Bugbot for commit ecdce6d. This will update automatically on new commits. Configure here.}