Cross platform dynamic assets

## Specific Demand

Different platforms deal with creating dynamic assets differently. Dioxus should provide a way to create a dynamic asset (like a generated image) that works on any platform.

## Implement Suggestion

Each renderer would need to implement dynamic assets differently:
- Web: use an [object url](https://developer.mozilla.org/en-US/docs/Web/API/URL/createObjectURL_static)
- Liveview: use a temporary asset url
- Fullstack: use a temporary asset url on the server, then if it is dynamically created on the client use a object url
- Desktop: use an asset url based on https://github.com/DioxusLabs/dioxus/pull/1719

Start by comparing how each renderer currently handles asset URLs, then review the desktop approach in pull request 1719. Trace the web, Liveview, Fullstack, and desktop renderer entry points before defining a shared dynamic-asset API. Done means generated assets work through the proposed platform-specific mechanisms across those renderers.

Written by the indexing model from the issue text.