codify "platform" into resolution logic, server-fn/fullstack overhaul (#4596)

overhaul dioxus fullstack using a new implementation of server_fn

This PR is a complete rewrite of dioxus fullstack designed to improve compatibility with axum and to fix a number of compilation errors based on feature flag unification plumbing through macros.

examples/07-fullstack/desktop/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "fullstack-desktop-example"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+dioxus = { workspace = true, features = ["launch", "fullstack"] }
+serde = { workspace = true }
+
+[features]
+default = []
+server = ["dioxus/server"]
+desktop = ["dioxus/desktop"]