Commit 6a26c59f removed Quickfix + QFGrep enhancement for
cscope since we wanted to use fzf and later skim. However,
since we now want to have as much as possible only pure
vimscript dependencies, reintroduce this so we need not
depend on fzf or any external fuzzy search tool anymore
with our recent usage of vim-clap.
Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>