llvm-context: lazy handling of function arguments and immutable data (#282)

- Lazily load function arguments so that they can be passed as pointers.
- Lazily call the immutable store function to avoid storing zero sized
immutable data.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/llvm-context/src/polkavm/evm/immutable.rs

@@ -257,6 +257,7 @@ where
             anyhow::bail!("Immutables are not available if the contract part is undefined");
         }
         Some(CodeType::Deploy) => {
+            context.enable_immutables();
             let immutable_data_pointer = context
                 .get_global(revive_runtime_api::immutable_data::GLOBAL_IMMUTABLE_DATA_POINTER)?
                 .value