Do not call initialize_block before any runtime api (#8953)

* Do not call `initialize_block` before any runtime api

Before this change we always called `initialize_block` before calling
into the runtime. There was already support with `skip_initialize` to skip
the initialization. Almost no runtime_api requires that
`initialize_block` is called before. Actually this only leads to higher
execution times most of the time, because all runtime modules are
initialized and this is especially expensive when the block contained a
runtime upgrade.

TLDR: Do not call `initialize_block` before calling a runtime api.

* Change `validate_transaction` interface

* Fix rpc test

* Fixes and comments

* Some docs

substrate/primitives/version/src/lib.rs

@@ -198,6 +198,11 @@ impl RuntimeVersion {
 	) -> bool {
 		self.apis.iter().any(|(s, v)| s == id && predicate(*v))
 	}
+
+	/// Returns the api version found for api with `id`.
+	pub fn api_version(&self, id: &ApiId) -> Option<u32> {
+		self.apis.iter().find_map(|a| (a.0 == *id).then(|| a.1))
+	}
 }
 
 #[cfg(feature = "std")]