feat(snap-networks-utils): add shared Asset UI component

[Julink-eth]

Explanation

This is the next step of consolidating the confirmation UI components across snaps, after EstimatedChanges (#369) and TransactionAlert (#408).
Every snap shows assets inline in its confirmation screens, for example in fee rows, operation parameters and ChangeTrust headers. Each one implements this separately:

• Stellar has Asset, AssetIcon and AssetText. Asset shows the fiat value (or a skeleton while prices load), a round icon with a question-mark fallback, then the amount and symbol, optionally as an explorer link. AssetIcon is also used on its own at xl size in the ChangeTrust headers.
• Tron has an Asset with the same layout. It shows a Snaps Icon instead of the image for bandwidth and energy fees, and doesn't support links.
• Solana has no component: its fee row in TransactionDetails builds the same layout by hand, without an icon.
  This PR adds shared Asset and AssetIcon components to @metamask/snap-networks-utils. As with the previous shared components, snaps pass display-ready values, and number and fiat formatting stay in each snap. Stellar takes prices as strings and Tron as numbers, so formatting can't be shared yet anyway.

AssetIcon is exported on its own (sizes sm, md, lg, xl) for standalone use like the Stellar ChangeTrust headers.
Stellar and Tron each ship a copy of the same question-mark SVG (identical file). It's now embedded once in the library as a string constant, because ts-bridge can't bundle .svg imports the way mm-snap does, and Snaps Image accepts raw SVG markup as src. I checked it matches the snaps' file apart from whitespace.
The snap migrations come in follow-up PRs, one per snap: Solana (fee row only), Stellar, then Tron.

References

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

[stanleyyconsensys]

Nice work
just some nit comment

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud