Support for double diamond input operator

[xsawyerx]

The double diamond (<<>>) input operator, introduced by @rgs in 5.22, provides a safer magic input operator that will not execute pipes as part of the input.

According to @Grinnz in Perl::Critic::Freenode, it gets parsed by PPI as two shift operators instead.

Here is the relevant output from PPI::Dumper:

  PPI::Statement
    PPI::Token::Operator    '<<'
    PPI::Token::Operator    '>>'