feat(printer): add cooling filter support flag and expose its toggle

cooling_filter_enabled existed as a config option but was shown nowhere,
and there was no capability flag to gate it. The cooling filter and air
filtration are alternative accessories sharing the same duct, so a
printer declares one or the other.

- new hidden printer capability flag support_cooling_filter
- "Use cooling filter" toggle in the Accessory group, shown only when
  the printer supports it; the air-filtration toggle hides in that case
  (no vendor restriction: third-party printers keep air filtration)
- explicit defaults (0) in the common machine base
- H2C declares support_cooling_filter=1 instead of support_air_filtration;
  its start-gcode already carries the cooling-filter conditional, so the
  toggle is functional. On H2C this drops the two exhaust-fan lines that
  air filtration emitted for ABS-class filaments, matching the printer's
  actual duct accessory; H2C is new on this branch so no existing user
  output changes.

Printers without the flag keep exactly the previous accessory UI and
g-code.

src/libslic3r/PrintConfig.hpp

@@ -1503,6 +1503,7 @@ PRINT_CONFIG_CLASS_DEFINE(
     ((ConfigOptionBool,                auxiliary_fan))
     ((ConfigOptionEnum<FanDirection>,  fan_direction))
     ((ConfigOptionBool,                support_air_filtration))
+    ((ConfigOptionBool,                support_cooling_filter))
     ((ConfigOptionBool,                cooling_filter_enabled))
     ((ConfigOptionEnum<PrinterStructure>,printer_structure))
     ((ConfigOptionBool,                support_chamber_temp_control))