Perl Mode - sub foo($) { broken

When a subroutine is declared, various symbols may
appear in the argument brackets to define the prototype
of the subroutine.

The symbols are:
$ : Scalar
@ : List
% : Hash
& : Anonymous subroutine
* : Typeglob

The current perl.xml highlighting breaks when $ is
included in the prototype. All of the other symbols are
handled correctly.

For example,

sub foo() {} is fine.
sub foo(%) {} is fine.
sub foo($) {} is broken as it interpreting $) as a
variable.
sub foo($$) {} appears fine, but is broken as the $$ is
highlighted as a variable, inconsistent with the other
symbols.

Otherwise, the current mode (#7773) is the best perl
mode we've had for ages - particularly since vanza
fixed 1585327!