[code_review] Improve Searchfox search by using "symbol" or "id" prefixes

[marco-c]

As suggested by @asutherland:

for something like this symbol search if you add the prefix "symbol:" if it's indeed a symbol or "id:" if it's an identifier search, things should go 1-to-2 orders of magnitude faster and greatly decrease the load on searchfox because you won't do a fulltext query. There's "docs" on all the search endpoint options in https://bugzilla.mozilla.org/show_bug.cgi?id=1762817#c0.