Some improvements to the boxed signatures in the docs (#6593)

* Show a more reasonable name in function docs

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Fix buggy docs for union types

Signed-off-by: Nick Cameron <nrc@ncameron.org>

* Make types in the docs signatures into links

Signed-off-by: Nick Cameron <nrc@ncameron.org>

---------

Signed-off-by: Nick Cameron <nrc@ncameron.org>

docs/kcl/std-math-atan2.md

@@ -8,11 +8,11 @@ Compute the four quadrant arctangent of Y and X.
 
 
 
-```js
+```kcl
 atan2(
-  y: number(Length),
-  x: number(Length),
-): number(rad)
+  y: [number](/docs/kcl/types/number)(Length),
+  x: [number](/docs/kcl/types/number)(Length),
+): [number](/docs/kcl/types/number)(rad)
 ```
 
 
@@ -30,7 +30,7 @@ atan2(
 
 ### Examples
 
-```js
+```kcl
 sketch001 = startSketchOn(XZ)
   |> startProfile(at = [0, 0])
   |> angledLine(