ParsedConstantDefinitions doesn’t support fully qualified constants

RuboCop::AST::Node#const_name doesn’t reveal whether a constant is fully qualified (e.g. ::HELLO) or not:

>> RuboCop::ProcessedSource.new('::HELLO', 2.6).ast.const_name
=> "HELLO"

>> RuboCop::ProcessedSource.new('HELLO', 2.6).ast.const_name
=> "HELLO"

As a result, the implementation of ParsedConstantDefinitions#collect_local_definitions is unaware of whether a constant is fully qualified, so it’s unable to put it in the correct namespace:

>> definitions = ParsedConstantDefinitions.new(
     root_node: parse_code('module Sales; ::HELLO = "World"; end')
   )
=> #<Packwerk::ParsedConstantDefinitions
     @local_definitions=
      {"::Sales"=>#<Parser::Source::Range (string) 7...12>,
       "::Sales::HELLO"=>#<Parser::Source::Range (string) 16...21>}>

>> definitions.local_reference?('HELLO')
=> false # should be true

>> definitions.local_reference?('Sales::HELLO')
=> true # should be false

I’m not going to fix this right now because I’m trying to make progress on a different task, but I think it’s a bug that’s going to affect users.

cc: @tomstuart

Start with ParsedConstantDefinitions#collect_local_definitions and reproduce the two fully qualified and unqualified constant examples from the issue. Trace how RuboCop::AST::Node#const_name is used, then verify that local_reference?('HELLO') and local_reference?('Sales::HELLO') produce the expected results for the module example.