ParserError#json_path raises NoMethodError when parsing with symbolize_names: true #1117

What happens

Since 3.1.0, calling json_path on a JSON::ParserError raised while parsing with symbolize_names: true raises NoMethodError as soon as the path contains an object key:

require "json"

begin
  JSON.parse('{"a": [1, {"b": xyz}]}', symbolize_names: true)
rescue JSON::ParserError => error
  error.json_path
end
# => undefined method 'valid_encoding?' for an instance of Symbol (NoMethodError)

Duplicate key errors in nested objects are affected the same way:

JSON.parse('{"x": {"a": 1, "a": 2}}', symbolize_names: true)
# rescue => error; error.json_path => NoMethodError

What should happen

error.json_path should return "$.a[1].b" (and "$.x.a" for the second example), as it does without symbolize_names.

Root cause

With symbolize_names: true the keys collected for the path are Symbols. ParserError#build_json_path accepts String and Symbol segments, but the check added in "Handle invalid encoding in JSON path keys" (#1113) calls segment.valid_encoding?, which only exists on String. Converting the segment with to_s before the checks fixes it.