Metaticket: priority symbolic functions implementations

[rwst]

This is a metaticket listing existing functions for which symbolic implementations are urgently needed because

• they exist in Sympy, Maxima, or Fricas symbolically, and might be returned as result
• they belong to the holonomic repertoire

special:

• Airy functions (Make Airy functions symbolic #12455)
• Kummer confluent hypergeometric functions (Implement symbolic confluent hypergeometric functions #14896)
• spherical Bessel and Hankel functions (Add Hankel functions and make spherical Bessel and Hankel functions symbolic #15024)

combinatorial:

• Bell numbers
• Bernoulli numbers
• Catalan numbers (Symbolic catalan number #22028)
• Fibonacci(n) (Symbolic fibonacci #22569), general Lucas(u,v)
• rising/falling/subfactorial (Pochhammer symbols #19461)

polynomial (metaticket #16670):

• Legendre P,Q (symbolic Legendre / associated Legendre functions / polynomials #16813)
• Laguerre (symbolic Laguerre / associated Laguerre polynomials #17151)
• GegenbauerC (Upgrade to Pynac-0.6.5 #20475)
• HermiteH (Upgrade to Pynac-0.6.5 #20475)
• JacobiP (Jacobi P polynomials without pexpect-maxima #22326)

Also the Dirichlet Eta function (#22146) which however is not holonomic.

Component: symbolics

Issue created by migration from https://trac.sagemath.org/ticket/17454