Check target compatibility before using the default renderer

[ealmloff]

Currently if you have a cargo.toml set up like this:

[dependencies]
dioxus = { version = "0.7.0-rc.0", features = ["router"] }

[features]
default = ["web"]
web = ["dioxus/web"]
desktop = ["dioxus/desktop"]

and serve with this command dx serve --platform desktop, dx will disable the web feature and enable the desktop feature flag because the renderer you selected was different than the default

However, that doesn't work if you serve with dx serve --destkop which only sets the target, not the renderer. This PR makes dx serve --desktop work by checking compatibility between the currently set target and the renderer. The implicit web renderer is not compatible with the explicitly set desktop target so dx disables the web renderer just like it does with --platform desktop

[jkelleyrtp]

I changed all the logic here in #4596 , the user will see different errors now