get_horz_ngrams works only when mention is_tabular

[HiromuHota]

Describe the bug

I have a span mention, mention, that is visual but is not tabular.
I tried to get all horizontally aligned ngrams from the same sentence (ie get_horz_ngrams(mention, from_sentence=False)), but I got none because it is not tabular.

To Reproduce
Steps to reproduce the behavior:

>>> mention = session.query(Mention).all()[0]
>>> print(mention.context.get_span())
Obama
>>> print(mention.context.sentence.text)
Obama was born in Honolulu, Hawaii.
>>> print(mention.context.sentence.is_visual())
True
>>> print(mention.context.sentence.is_tabular())
False
>>> from fonduer.utils.data_model_utils.visual import get_horz_ngrams
>>> print(list(get_horz_ngrams(mention, from_sentence=False)))
[]

Expected behavior

Since all the other 1-gram in the same sentence is horizontally aligned with the mention, I want to get all those.

>>> print(list(get_horz_ngrams(mention, from_sentence=False)))
["was", "born", "in", "Honolulu", ",", "Hawaii", "."]

Error Logs/Screenshots
If applicable, add error logs or screenshots to help explain your problem.

Environment (please complete the following information):

• OS: N/A
• PostgreSQL Version: N/A
• Poppler Utils Version: N/A
• Fonduer Version: 0.8.2

Additional context
Add any other context about the problem here.

In addition to the above issue, I feel from_sentence is a bit confusing.

[HiromuHota]

Oh, I just found a TODO comment

fonduer/src/fonduer/utils/data_model_utils/visual.py

Lines 230 to 240 in faae9c2

	def _get_direction_ngrams(
	direction: str,
	c: Union[Candidate, Mention, TemporarySpanMention],
	attrib: str,
	n_min: int,
	n_max: int,
	lower: bool,
	from_sentence: bool,
	) -> Iterator[str]:
	# TODO: this currently looks only in current table;
	# precompute over the whole document/page instead