Improve default matching behavior for VIP Enterprise Search

[dlh01]

Originally reported by @scottnelle in an internal Alley repo:

VIP Enterprise search seems to default to phrase matching which requires that all terms in the query (or maybe even the entire exact phrase) appears in a field for an article to match. This makes longer search phrases very unlikely to match any articles. For example, on a site that is almost entirely about home improvement, the phrase "how to paint my house" yields zero results because the writing is rarely in first person.

We should apply a more flexible default query type, perhaps inspired by the defaults set in SearchPress https://github.com/alleyinteractive/searchpress/blob/d7feab20ee2214caa574e410d535414978c00182/lib/class-sp-wp-search.php#L250-L251

[scottnelle]

Worth confirming whether this is still true before going too far down this road. The default behavior at the time was so unhelpful that I'm surprised it shipped, and it's entirely possible it's been updated since then, or that it was a glitch in the setup of the individual site.