Add error position and json_path to the JRuby extension

[ojuschugh1]

Follow-up to #1062, as suggested there: this brings ParserError#line, #column and #json_path to the JRuby extension.

The Java parser already shares the C parser's architecture (frame stack + value stack), so the implementation mirrors it closely: positions are computed by scanning backwards from the error offset like cursor_position does in C, and @json_path is collected as raw segments from the frame stack, then formatted by the shared Ruby code from #1062. Everything happens at raise time, so nothing is added to the happy path. NestingError stays bare, matching the C extension.

Positions and paths come out identical to the C parser:

**jruby 10.0.2.0**
unexpected token at 'xyz}]}}' at line 1 column 34
line=1 column=34 json_path=$.user.roles[1].admin
duplicate key "c" at line 1 column 17
line=1 column=17 json_path=$.a.b[1].c

​
The duplicate key case reuses the existing cursor rewind to the object's opening brace, so line/column match C exactly there too. Error message wording still differs between the two extensions ("unexpected token at" vs "unexpected character:"); I left that alone to keep the diff focused.

The four json_path test methods now run on JRuby (omit guards removed), plus a new test_parse_error_position asserting line/column values on both extensions. JRuby suite goes from 53 omissions to 49 with 0 failures; CRuby stays at 0 failures, 0 omissions.