feat: add ffi get mnemonic wordlist

[hansieodendaal]

Description

Added an FFI method to get the entire mnemonic word list for a given language.

Motivation and Context

See above.

How Has This Been Tested?

• Added a unit test to test this functionality.
• Added a cucumber test to verify the mnemonic word list is retrieved.

[hansieodendaal]

Although TariSeedWords and TariMnemonicWordList looks the same, they are different things. All methods that operate on TariSeedWords is not valid for TariMnemonicWordList, for example seed_words_push_word. One might retrieve the mnemonic word list and then continue to work with it as if it is the seed words.

[philipr-za]

Although TariSeedWords and TariMnemonicWordList looks the same, they are different things. All methods that operate on TariSeedWords is not valid for TariMnemonicWordList, for example seed_words_push_word. One might retrieve the mnemonic word list and then continue to work with it as if it is the seed words.

So you would rather repeat all the helper functions except that single one (which returns feedback that something is wrong)? We are dealing with a very clunky FFI interface here which is unsafe on many levels so needs careful handling by the client and this is a case where I believe that adding 3 completely repeated helpers functions for a SLIGHTLY more appropriate API interface is definitely the wrong move.

Edit: To be clear the original PR already missed 2 of these functions which was get_length and get_at. I feel this already demonstrates the issue of adding more types that are not really necessary.

[hansieodendaal]

Thank you @delta1, @philipr-za and @StriderDM for the review comments; applied all. Unit tests and cucumber test working properly.

[hansieodendaal]

@StriderDM the code panics if position == len, thus the change from> to >=. I tested this by accident.

        if position >= len as u32 {
            error = LibWalletError::from(InterfaceError::PositionInvalidError).code;
            ptr::swap(error_out, &mut error as *mut c_int);
        } else {
            word = CString::new((*seed_words).0[position as usize].clone()).unwrap()
        }

[StriderDM]

@hansieodendaal Good find. Yeah I realized that right after posting my comment.

Addressed and holding up merge queue maybe