Size the prime tower from the actual flush volumes

Prime towers reserved depth from the prime volume alone, ignoring the flush
matrix: rib-wall towers in both the engine and the preview, and rectangle and
cone towers in the preview, which never carried the flush-aware estimate the
engine already used. The preview also read the print preset, which does not
carry the printer- and filament-scope keys the estimate needs and so silently
fell back to defaults. On multi-nozzle printers the flush matrix, which holds
one block per nozzle, was additionally read as a single block. The tower could
come out too small for the purge it has to hold.

The flush-based estimate also skipped the height-based minimum depth that the
prime-volume one applies, so low-flush prints could estimate a tower shallower
than the one that actually gets built.

src/libslic3r/GCode/WipeTower2.hpp

@@ -17,6 +17,7 @@ namespace Slic3r
 
 class WipeTowerWriter2;
 class PrintRegionConfig;
+class ConfigBase;
 
 class WipeTower2
 {
@@ -26,7 +27,10 @@ public:
     // in WipeTowerIntegration::append_tcr2 does not strip it.
     static const std::string wait_for_temp_tag() { return ";_WAIT_FOR_TEMP_ON_WIPE_TOWER"; }
 	static std::pair<double, double> get_wipe_tower_cone_base(double width, double height, double depth, double angle_deg);
-	static std::vector<std::vector<float>> extract_wipe_volumes(const PrintConfig& config);
+	static std::vector<std::vector<float>> extract_wipe_volumes(const ConfigBase& config);
+	// Estimated total flush volume of a SEMM print with the given number of filaments,
+	// used to reserve wipe tower space before the tower is generated.
+	static float estimate_semm_flush_volume(const ConfigBase& config, size_t filaments_cnt);
 
     
     // Construct ToolChangeResult from current state of WipeTower2 and WipeTowerWriter2.