[This is preliminary documentation and subject to change.]
Write the Sample File Table out.
This is only relevant for an inline file. With a detached file, this can be called but does nothing. The first time this is called (on a Choon instance) this writes a placeholder SFT (with the correct number of samples) and marks the position.
Subsequent calls write current SFT data at this position.
A typical converter calls this once after saving Meta and then calls End to finish up.