R1:c662dda0f17d

When selecting Ferret ngrams, select term ngrams (not raw ngrams) for term search

Summary:
Ref T12819. For queries like `v0.2`, we would incorrectly search for ngrams including `0.2`, but this is only a substring ngram: the term corpus splits this into `v0` and `2`, so `0.2` is not in the ngrams table.

When executing term queries, search for term ngrams instead. This makes "v0.2" work properly again.

Test Plan: Searched for "v0.2", found a task with "v0.2" in the title.

Reviewers: chad

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