[ruby/rdoc] Fix ToRdoc generating incorrect {label,name}-lists

Previously, trying to round-trip label-list and name-lists with the
ToRdoc converter was not possible:

```ruby
doc = <<~RDOC
foo ::
bar ::
  hi
RDOC

markup = RDoc::Markup.parse(doc)
markup # => [doc: [list: NOTE [item: ["foo ", "bar"]; [para: "hi"]]]]

rt = RDoc::Markup::ToRdoc.new.convert(markup)
rt # => "foo\nbar:\n  hi\n\n"

rt_markup = RDoc::Markup.parse(rt)
rt_markup # => [doc: [para: "foo ", "bar:"], [verb: "hi\n"]]
```

This commit addresses the issue by fixing ToRdoc to generate output that
can be properly reparsed by RDoc. ToRdoc tests additionally needed to be
updated for the new output.

The old implementation of `accept_list_item_start` was copied to ToBs
because those tests did not pass with the new changes and I am
unfamiliar with the `backspace` format.

After:

```ruby
doc = <<~RDOC
foo ::
bar ::
  hi
RDOC

markup = RDoc::Markup.parse(doc)
markup # => [doc: [list: NOTE [item: ["foo ", "bar"]; [para: "hi"]]]]

rt = RDoc::Markup::ToRdoc.new.convert(markup)
rt # => "foo::\nbar::\n  hi\n\n"

rt_markup = RDoc::Markup.parse(rt)
rt_markup # => [doc: [list: NOTE [item: ["foo", "bar"]; [para: "hi"], blankline]]]
```

https://github.com/ruby/rdoc/commit/c6c51aa900

0 files changed, 0 insertions, 0 deletions