message: doc(runtime-core) Add missing doc on `vm::FuncCtx`.
diff: @@ -551,14 +551,17 @@ pub struct FuncCtx {
  }
  impl FuncCtx {
  + /// Offset to `vmctx`.
  pub fn offset_vmctx() -> u8 {
  0 * (mem::size_of::<usize>() as u8)
  }
  + /// Offset to `func_env`.
  pub fn offset_func_env() -> u8 {
  1 * (mem::size_of::<usize>() as u8)
  }
  + /// Size of a `FuncCtx`.
  pub fn size() -> u8 {
  mem::size_of::<Self>() as u8
  }
  