bug#43916: $$, $@, $bla colors in Perl mode vs. Shell-script mode

[積丹尼 Dan Jacobson]

Looking at
print $$, $@, $bla
in Shell-script mode and Perl mode:
At least all three leading $ should look the same in the same file.
And they should all either be the same color, or different colors, from what
follows them.
So Perl mode has some work to do.
emacs-version "26.3"