Finish merge with C API refactor

lib/c-api/src/wasm_c_api/wasmer.rs

@@ -0,0 +1,9 @@
+//! Wasmer-specific extensions to the Wasm C API.
+
+use crate::wasm_c_api::instance::wasm_instance_t;
+use std::ffi::c_void;
+
+#[no_mangle]
+pub unsafe extern "C" fn wasm_instance_get_vmctx_ptr(instance: &wasm_instance_t) -> *mut c_void {
+    instance.inner.vmctx_ptr() as _
+}