Replace the FLAC encoder library with an own implementation

[douglas-carmichael]

Problem

The bundled FLAC encoder library crashes with an ArrayIndexOutOfBoundsException (in Subframe_Fixed.encodeSamples) on any sample whose length modulo 4096 is 2, 3 or 4 and whose trailing samples are not all identical: the fixed-predictor order selection reads 4 samples ahead without checking the length of the final short block. A real-world example is a 65538-frame drum sample (16 × 4096 + 2).

Affected writers:

• Renoise: falls back to storing the sample as uncompressed WAV inside the XRNI ('The FLAC encoder failed for sample ...').
• SFZ (FLAC option), Bliss, Synclavier Regen: no fallback existed, the preset failed; for Synclavier Regen a fallback is not even possible since SFLC files must be FLAC.

Solution

A new encoder file/flac/FlacEncoder written from the FLAC specification (RFC 9639), in the same spirit as the existing NCW/SF2/RIFF/FastLZ implementations. It supports constant, verbatim, fixed prediction (order 0-4) and linear prediction (LPC, order up to 8) sub-frames, Rice coding with per-partition parameters and per-frame stereo de-correlation (left/side, side/right, mid/side), each chosen by the smallest encoded size. Compression is on par with the old library (within ~2% on a real drum library); losslessness is guaranteed by construction since the residuals are calculated with the exact integer arithmetic of the decoder. Short trailing blocks - the case the old library crashed on - are handled correctly for all lengths.

The library remains in use for reading FLAC files. Two quirks of its jFLAC based reader are deliberately catered for so ConvertWithMoss can re-read its own output: a PADDING block always terminates the meta-data (the reader fails if STREAMINFO is the only block) and blocks shorter than 16 samples are stored verbatim (the reader mis-decodes predicted sub-frames there). AudioFileUtils.compressToFLAC now returns the bytes directly, which also removes the temporary-file workarounds in the Renoise, Bliss and Synclavier Regen creators.

Verification

• 36-file test matrix (every trailing-block length 0-15 plus longer ones, 1-5 frame files, 8/16/24 bit, mono/stereo, correlated stereo, silence, noise, odd sample rates, 32-bit int/float sources): every file passes flac -t (flac 1.5.0, including its MD5 check of the decoded audio), decodes byte-identical with the reference decoder and round-trips through the application's own FLAC reader.
• A 1277-sample Decent Sampler drum library (which triggered the original crash) converts to Renoise with all samples as valid FLAC and no WAV fallbacks.