Moves runtime macro out of experimental flag (#4249)

Step in https://github.com/paritytech/polkadot-sdk/issues/3688

Now that the `runtime` macro (Construct Runtime V2) has been
successfully deployed on Westend, this PR moves it out of the
experimental feature flag and makes it generally available for runtime
devs.

---------

Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

prdoc/pr_4249.prdoc

+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Moves runtime macro out of experimental flag
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      Now that the runtime macro (Construct Runtime V2) has been successfully deployed on Westend, 
+      this PR moves it out of the experimental feature flag and makes it generally available for
+      runtime devs.
+
+crates:
+  - name: frame-support
+    bump: minor
+  - name: frame-support-procedural
+    bump: minor

substrate/frame/support/procedural/src/lib.rs

@@ -1249,7 +1249,6 @@ pub fn import_section(attr: TokenStream, tokens: TokenStream) -> TokenStream {
 ///
 /// * The macro generates a type alias for each pallet to their `Pallet`. E.g. `type System =
 ///   frame_system::Pallet<Runtime>`
-#[cfg(feature = "experimental")]
 #[proc_macro_attribute]
 pub fn runtime(attr: TokenStream, item: TokenStream) -> TokenStream {
 	runtime::runtime(attr, item)

substrate/frame/support/procedural/src/runtime/mod.rs

@@ -200,8 +200,6 @@
 //!     +----------------------+
 //! ```
 
-#![cfg(feature = "experimental")]
-
 pub use parse::Def;
 use proc_macro::TokenStream;
 use syn::spanned::Spanned;

substrate/frame/support/src/lib.rs

@@ -508,7 +508,6 @@ pub use frame_support_procedural::{
 	construct_runtime, match_and_insert, transactional, PalletError, RuntimeDebugNoBound,
 };
 
-#[cfg(feature = "experimental")]
 pub use frame_support_procedural::runtime;
 
 #[doc(hidden)]