MDC-101: Wrong method to read the input character

[TonyGuyot]

The MDC-101 Codelab is using the setOnKeyListener method to detect the characters typed into the password text field. That method does not work with a soft input keyboard (what one mostly used on an Android device) but only with a hardware keyboard.

The right solution is to use a TextWatcher like that:

        // Clear the error once more than 8 characters are typed.
        val watcher = object : TextWatcher {
            override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
            }

            override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
            }

            override fun afterTextChanged(s: Editable?) {
                if (isPasswordValid(password_edit_text.text)) {
                    // Clear the error.
                    password_text_input.error = null
                }
            }
        }
        view.password_edit_text.addTextChangedListener(watcher)