WebP support for resizetizer

### Description

Currently, when MAUI generates images from SVG it creates PNGs. Recently, when releasing our app, I noticed a recommendation to use WebP format instead to lower the app size.


Not something I think is super important as the gain is marginal, but would be good to keep in mind.

### Public API Changes

Maybe a new csproj variable to enable the extra conversion from png to WebP, to avoid breaking changes.

### Intended Use-Case

Lower app size, potentially improve performance

Start by locating MAUI's resizetizer and its SVG-to-PNG image-generation flow, then inspect how project-file properties configure that process. Define the supported WebP conversion behavior and an opt-in configuration before implementing it; done means generated assets can use WebP and the app-size use case is covered.

Written by the indexing model from the issue text.