Fix for #35332.

Fix for #35332.
The problem is caused by the user mixing positional and named parameters.
PDO was blindly adding the parameters, unaware that the same parameters were
already allocated by position.

What we do now is register the parameter with the driver before adding it to
any hash.  This gives the driver an opportunity to normalize the name and
parameter number.  PDO can then ensure that only one entry is occupied in the
hash for a given parameter.