Svexs-length
Get the length of the svexarr array.
In the execution this just gets the array length. The
logical definition is just a wrapper for len:
Function: svexs$a-length
(defun svexs$a-length (svexarr$a)
(declare (xargs :guard (svexarr$ap svexarr$a)))
(len svexarr$a))
