Add LinkBatch to Special:LinkSearch

When building the result list, each link results in a database query.
The select is on the page table, so it is known, that each page exists,
but using Linker::linkKnown does not prepare the link for stubthreshold
or redirect marker.

Change-Id: I8f73d398f510f252ac8d5a0fd04ccb0feaf79cc4
Merge "Add LinkBatch to Special:LinkSearch"