Blazor static SSR additional FormMapping options: TrimFormValues & TreatEmptyStringAsNull

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

_No response_

### Describe the solution you'd like

It can be a handy thing to have these 2 additional Blazor Forms Mapping options or maybe getting an access to the FormMapping Factories, Converters and other things.
For example, with MVC we have this workaround [to register a custom ModelBinder to trim any model string values automatically](https://stackoverflow.com/a/75039213/22411744).

### Additional context

_No response_