Airy function cleanup (#18050)

This rearranges the different airy functions, deprecating `airy`, `airyx` and `airyprime` in favour of the more specific variants (`airyai`, `airyaiprime`, etc.), and clarifies the docs of each remaining function. Fixes #17032.

Author: simonbyrne

docs/src/special.md

@@ -184,13 +184,14 @@ Base.Math.digamma
 Base.Math.invdigamma
 Base.Math.trigamma
 Base.Math.polygamma
-Base.Math.airy
 Base.Math.airyai
-Base.Math.airyprime
 Base.Math.airyaiprime
+Base.Math.airyaix
+Base.Math.airyaiprimex
 Base.Math.airybi
 Base.Math.airybiprime
-Base.Math.airyx
+Base.Math.airybix
+Base.Math.airybiprimex
 Base.Math.besselj0
 Base.Math.besselj1
 Base.Math.besselj