adds feature server_fn_axum that compiles for wasm target (#3840)

The current `axum` feature and `server` feature are incompatible with wasm32-unknown-unknown target
due to:
1. depends on axum features not compatible with wasm
2. SSR requires reading the filesystem for index.html

With this patch I add the `server_fn_axum` feature which disables SSR and enables targeting
wasm32-unknown-unknown with server functions enabled.

Note that for this to work, `server_fn` depends on `inventory` and as stated in this docs depending on
the context you might need to expose and call [`__wasm_call_ctors`](https://docs.rs/inventory/latest/inventory/#webassembly-and-constructors)
(I needed that specifically for cloudflare workers)

change axum_server_fn feature for axum_wasm and include SSR tools there

This change additionaly make axum_server_fn feature additive by exposing a different
`DioxusRouterWasmExt` with only the wasm-compatible parts instead of exposing the
`DioxusRouter` trait under the same name.

Docs are updated to reflect this change.

rename axum_wasm to axum_core and update docs

fix typo

re-enable default-features for axum in dioxus-cli

re-enable axum default-features for liveview

re-enable default-features for axum for playwright-tests

packages/liveview/Cargo.toml

@@ -33,7 +33,7 @@ dioxus-cli-config = { workspace = true }
 generational-box = { workspace = true }
 
 # axum
-axum = { workspace = true, optional = true, features = ["ws"] }
+axum = { workspace = true, optional = true, default-features = true, features = ["ws"] }
 
 [dev-dependencies]
 tokio = { workspace = true, features = ["full"] }