Can FST read bytes forward?

### Description

Forked from https://lists.apache.org/thread/1fskhmz84pp60o41txsxj2193vt9txod: the fact that FST reads bytes backwards doesn't play well with BufferedIndexInput, which triggers a refill on every byte read. Could we reverse these sequences of bytes at index time so that they would be read in forward order at search time?

Start by tracing how FST reads byte sequences and how BufferedIndexInput refills during those reads; the issue identifies index time and search time as the relevant phases. Compare the current backward-read behavior with forward reads and determine whether the proposed ordering avoids a refill on every byte without breaking search results.

Written by the indexing model from the issue text.