feat(Geometry/Euclidean): volume of a simplex

Author: wwylele

Mathlib.lean

@@ -4310,6 +4310,7 @@ public import Mathlib.Geometry.Euclidean.Sphere.Ptolemy
 public import Mathlib.Geometry.Euclidean.Sphere.SecondInter
 public import Mathlib.Geometry.Euclidean.Sphere.Tangent
 public import Mathlib.Geometry.Euclidean.Triangle
+public import Mathlib.Geometry.Euclidean.Volume.Integral
 public import Mathlib.Geometry.Euclidean.Volume.Measure
 public import Mathlib.Geometry.Group.Growth.LinearLowerBound
 public import Mathlib.Geometry.Group.Growth.QuotientInter