Tune Perl/Raku heuristics

[mauke]

Closes #6263.

Description

• Relax Perl pattern: use 5; and use v5; are acceptable (no . required).

• Treat use constant and use overload as Perl; Raku has different mechanisms for constants and operator overloading.

• Treat assignments to @EXPORT as Perl (Raku has a different symbol export mechanism):

  our @EXPORT = (...);
  @EXPORT = (...);
  *EXPORT = [...];

• Treat package declarations as Perl, not Raku:

  package Foo::Bar;
  package Foo::Bar v1.2.3;
  package Foo::Bar 1.05;
  package Foo::Bar { ... }

• As a last resort, recognize the use of -> for dereferencing and method calls as indicative of Perl (Raku uses . for methods and has no references):

  Some::Class->class_method
  $some_variable->method
  $Some::Class::variable->method
  $array_reference->[0]
  $hash_reference->{key}
  $code_reference->(@arguments)

Checklist

• I am fixing a misclassified language
  • I have included a new sample for the misclassified language:
    • Sample source(s): N/A (original)
    • Sample license(s): MIT
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

[lildude]

LGTM. Thanks.

Note: this PR will not be merged until close to when the next release is made. See here for more details.