feat: add std.atan2

Fixes: #141
Fixes: google/jsonnet#1118

Author: CertainLach

crates/jrsonnet-stdlib/src/lib.rs

@@ -104,6 +104,7 @@ pub fn stdlib_uncached(settings: Rc<RefCell<Settings>>) -> ObjValue {
 		("asin", builtin_asin::INST),
 		("acos", builtin_acos::INST),
 		("atan", builtin_atan::INST),
+		("atan2", builtin_atan2::INST),
 		("exp", builtin_exp::INST),
 		("mantissa", builtin_mantissa::INST),
 		("exponent", builtin_exponent::INST),

crates/jrsonnet-stdlib/src/math.rs

@@ -89,6 +89,11 @@ pub fn builtin_atan(x: f64) -> f64 {
 	x.atan()
 }
 
+#[builtin]
+pub fn builtin_atan2(y: f64, x: f64) -> f64 {
+	y.atan2(x)
+}
+
 #[builtin]
 pub fn builtin_exp(x: f64) -> f64 {
 	x.exp()