some LSPs does update the active signature and some not. To make both
worlds happy, make the active signature more intelligent.
1. SignatureHelp store now the suggested lsp_signature
2. if the lsp_signature changes then use it
3. otherwise use the last signature from the old popup
4. in case the old signature doesn't exist anymore, show the last signature
Signed-off-by: Ben Fekih, Hichem <hichem.f@live.de>
implement handle_event to cycle through the function signatures.
To change the signature press alt+p/n .
Signed-off-by: Ben Fekih, Hichem <hichem.f@live.de>
