Feat: hide double underscored symbols from symbol search
Fixes#17272 by changing the default behavior of query to skip results that start with `__` (two underscores).
Not sure if this has any far reaching implications - a review would help to understand if this is the right place to do the filtering, and if it's fine to do it by default on the query.
If you type `__` as your search, then we'll show the matching double unders, just in case you actually need the symbol.
6bae8e333b