[chains] Bug 445843: Quick fix is obscured by alternative method recommendation

Also fixes Bug 438293. Chain proposals now have a relevance of the
negative chain size. Before it was (2 xor 12) - chain size, which
doesn't make a lot of sense. This ensures that the proposals are below
standard proposals in both quickfix and content assist.

Signed-off-by: Johannes Dorn <johannes.dorn@codetrails.com>