void putFormatter(Character identifier, BiFunction<Object, String, String> formatFunction) {
            if (Arrays.binarySearch(VALID_FORMATTER_CHARS, identifier) < 0) {
                throw new IllegalArgumentException("Invalid formatter identifier: " + identifier);
            }
            formatters.put(identifier, formatFunction);
        }
Inline states are created when formatting text. They aren't written
directly to the AbstractCodeWriter, but rather captured as part of the
process of expanding a template argument.
smithy-utils/src/main/java/software/amazon/smithy/utils/AbstractCodeWriter.java