client: For filter, prioritize exact, startsWith

client: For filter, prioritize exact, startsWith

When filtering buffer view results, prioritize exact string matches,
then prioritize startsWith matches, both case-insensitive.  Within
these results, sort normally (e.g. alphabetical).

This gives weight to exact matches and the start of the string.  When
no filter string is specified, sorting goes back to normal.

Search string: "car"
Before:
> acar
> bcar
> careful
> caring
> racecar
> car [hidden]

After:
> car [hidden]
> careful
> caring
> acar
> bcar
> racecar

Where [hidden] represents a buffer that's temporarily or permanently
hidden.