Verify WipeTower Footprint at Point of Generation

The clamps and validation work from estimates. Once the tower is
generated, _make_wipe_tower re-tests the exact first-layer footprint,
brim and cone base included, against the printable area and the
exclusion zone, so an off-plate tower fails with a clear error instead
of exporting unprintable G-code. The rectangle-wall mesh footprint
learns the Type2 cone base so that check and the post-generation
validation see the real outline.

Pre-generation, validation hard-checks the body plus an explicit brim
and warns on the estimated auto brim and cone base with the existing
"may collide" strings, so the user hears about a marginal position on
the first slice rather than only at generation time.

Two fff_print fixtures that print a tower at the default position move
it onto the 200 mm test bed, as the multifilament fixtures already do:
the shipped default y of 220 is off that bed, and the backstop now says
so instead of exporting the tower.

tests/fff_print/test_gcodewriter.cpp

@@ -574,6 +574,9 @@ static DynamicPrintConfig dual_extruder_toolchange_config()
     config.set_key_value("nozzle_temperature_range_high", new ConfigOptionInts({240, 240}));
     config.set_key_value("flush_multiplier",     new ConfigOptionFloats({1}));
     config.set_key_value("flush_volumes_matrix", new ConfigOptionFloats({0, 140, 140, 0}));
+    // Inside the 200x200 test bed; the default y, 220, is not, and generation rejects that.
+    config.set_key_value("wipe_tower_x",         new ConfigOptionFloats({50.}));
+    config.set_key_value("wipe_tower_y",         new ConfigOptionFloats({50.}));
     return config;
 }