Add new cconv-tests (Bug#28557)

Add new cconv-tests (Bug#28557)

These tests are all written by Gemini Lasswell <gazally@runbox.com>.

* test/lisp/emacs-lisp/cconv-tests.el
(top-level): Add two commented out tests which the byte-compiler
can't handle.
(cconv-tests-lambda-:documentation)
(cconv-tests-pcase-lambda-:documentation)
(cconv-tests-defun-:documentation)
(cconv-tests-cl-defun-:documentation)
(cconv-tests-function-:documentation)
(cconv-tests-cl-defgeneric-literal-:documentation)
(cconv-tests-defsubst-:documentation)
(cconv-tests-cl-defsubst-:documentation): New tests.
(cconv-tests-cl-iter-defun-:documentation)
(cconv-tests-iter-defun-:documentation)
(cconv-tests-iter-lambda-:documentation)
(cconv-tests-cl-function-:documentation)
(cconv-tests-cl-defgeneric-:documentation): New failing tests.