Rename userdata to data (#3282)

* Rename userdata to data

Instead of saying "userdata", which is ambiguous and imprecise,
say "instruction data" or "account data".

Also, add `ProgramError::InvalidInstructionData`

Fixes #2761

sdk/src/native_loader.rs

@@ -18,7 +18,7 @@ pub fn create_program_account(name: &str) -> Account {
     Account {
         lamports: 1,
         owner: id(),
-        userdata: name.as_bytes().to_vec(),
+        data: name.as_bytes().to_vec(),
         executable: true,
     }
 }