[clangd] Extract scoring/ranking logic, and shave yaks.

Summary:
Code completion scoring was embedded in CodeComplete.cpp, which is bad:
 - awkward to test. The mechanisms (extracting info from index/sema) can be
   unit-tested well, the policy (scoring) should be quantitatively measured.
   Neither was easily possible, and debugging was hard.
   The intermediate signal struct makes this easier.
 - hard to reuse. This is a bug in workspaceSymbols: it just presents the
   results in the index order, which is not sorted in practice, it needs to rank
   them!
   Also, index implementations care about scoring (both query-dependent and
   independent) in order to truncate result lists appropriately.

The main yak shaved here is the build() function that had 3 variants across
unit tests is unified in TestTU.h (rather than adding a 4th variant).

Reviewers: ilya-biryukov

Subscribers: klimek, mgorny, ioeric, MaskRay, jkorous, mgrang, cfe-commits

Differential Revision: https://reviews.llvm.org/D46524

llvm-svn: 332378

0 files changed, 0 insertions, 0 deletions