bug#45255: cperl-mode doesn't recognise the double diamond operator

[E. Choroba]

Perl 5.22 added the new form of the diamond operator <<>> (which uses the
three argument version of open under the hood).

Unfortunately, cperl-mode doesn't recognise it and treats it as a HERE-doc
start:

while (<<>>) {
This is displayed in the font-lock-string-face.
The here document ends with an empty line.
Pressing Tab doesn't indent the code.

Ch.