windows-reactor: add more windows-reactor: resources()

[kouhe3]

Suggestion

ElementExt::resources() on windows-reactor currently accepts only (String, String).

I want to draw red button like windows terminal

microsoft-ui-reactor ships Resources(r => r.Set("ButtonBackground", "#B22222")) with ResourceBuilder supporting colors/brushes/ThemeRef/doubles/CornerRadius

So I need this feature

[Tam1SH]

Regarding resource editing, I'd like to have access at the application level too — currently in windows-reactor the API is restricted via pub(crate) on IApplication::Resources and Application::Current. Would it be possible to expose these as pub?