Apply Options.DirectoryFilters when searching for workspace symbols.
The natural way to implement it would lead to an import loop, so
the working code was moved from cache to source.
Fixesgolang/go#48939
Change-Id: Iccf32bc8327ba7845505a6a3de621db8946063f5
Reviewed-on: https://go-review.googlesource.com/c/tools/+/359514
Run-TryBot: Peter Weinberger <pjw@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Peter Weinberger <pjw@google.com>
Reviewed-by: Suzy Mueller <suzmue@golang.org>