math: Add trigonometric functions and some angle helper functions

This commit adds these new template functions in the `math` namespace:

math.Acos
math.Asin
math.Atan
math.Atan2
math.Cos
math.Pi
math.Sin
math.Tan
math.ToDegrees
math.ToRadians

Co-authored-by: Joe Mooring <joe@mooring.com>

docs/content/en/functions/math/Pi.md

@@ -0,0 +1,24 @@
+---
+title: math.Pi
+description: Returns the mathematical constant pi.
+categories: []
+keywords: []
+action:
+  aliases: []
+  related:
+    - functions/math/Sin
+    - functions/math/Cos
+    - functions/math/Tan
+    - functions/math/Asin
+    - functions/math/Acos
+    - functions/math/Atan
+    - functions/math/Atan2
+  returnType: float64
+  signatures: [math.Pi]
+---
+
+{{< new-in 0.130.0 >}}
+
+```go-html-template
+{{ math.Pi }} → 3.141592653589793
+```