MilkDrop fidelity: missing keys and values that stay in the file

[CaYatur]

What

This is the third #580 change. It covers missing keys and the values MilkDrop keeps out of the equations. Everything was checked against Nullsoft's code (jecassis/foo_vis_milk2 5b44cea) and the D3D9 code (BeatDrop 53d83ee), and all of it sits behind the fidelity switch.

• Missing wave colour and position. MilkDrop reads a missing wave_r, wave_g, wave_b, wave_x or wave_y with rot's value as the default (state.cpp:1389-1393). rot is still 0 at that point, so a file without these keys draws a black wave in the corner. The engine drew it white and centred.
• Missing shape colours. Custom shapes are red inside and green, transparent, outside (state.cpp:619-626). The engine used white and black.
• Values that stay in the file. Wave scale and smoothing, the volume fade's switch and range, warp speed and warp scale are not per-frame variables in MilkDrop. The engine read them from per-frame values, with || 1 fallbacks. They now come from the file:
  • missing smoothing is 0.75, and the fade range is 0.75 to 0.95;
  • a wave scale of 0 flattens the wave (102 corpus presets), where || 1 turned it into 1;
  • a warp speed of 0 stops the warp pattern (4 presets), where || 1 turned it into 1;
  • through a transition they blend linearly;
  • warp speed and scale come from the new preset for both meshes, because MilkDrop computes the warp once per frame from the new state (milkdropfs.cpp:1591-1597);
  • a custom wave takes the wave scale of its own preset, unblended (2429).

No corpus preset leaves out the keys in the first two bullets, and neither do ours.

Measured

Against main, over the last 10 of 60 frames:

• Control presets: 120 of 120 identical.
• Wave scale 0: 12 of 102 change, 7 of them by more than 1% (up to 23%), because their waves are now flat.
• Warp speed 0: 1 of 4 changes, slightly.
• Fidelity off: everything is byte-identical.
• 900-preset sample: the same classes, preset for preset.

Tests

• 3 new tests, and 5 test files updated to the new reads; 16 of 16 mutations are caught.
• npm test: 2187 of 2187 pass, and each commit passes on its own. The changed files also pass under Linux emulation.
• npm run smoke: PASS, with the userData checksums unchanged.

Refs #580
Refs #560