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/api/proc-macro/src/mock_impl_runtime_apis.rs

@@ -94,6 +94,13 @@ fn implement_common_api_traits(
 				Ok(pred(A::VERSION))
 			}
 
+			fn api_version<A: #crate_::RuntimeApiInfo + ?Sized>(
+				&self,
+				_: &#crate_::BlockId<#block_type>,
+			) -> std::result::Result<Option<u32>, #crate_::ApiError> where Self: Sized {
+				Ok(Some(A::VERSION))
+			}
+
 			fn record_proof(&mut self) {
 				unimplemented!("`record_proof` not implemented for runtime api mocks")
 			}