Add an option to ignore {,re}trigger characters for signatureHelp

[griwes]

Currently, the plugin only invokes textDocument/signatureHelp when at a trigger character (or at retrigger if already active). This is fine when initially typing a function call, but if you need to edit the middle of an argument, signature help will not trigger, and that would often be helpful.

Therefore - can we get an option to ignore the server provided trigger characters and always trigger signatureHelp on InsertEnter, CursorMovedI, and TextChangedI? This could be worked around with some autocmds, but it'd be much more elegant to do in the plugin itself.

[griwes]

Hmm, actually, autocmd InsertEnter * lua require('blink.cmp.trigger.signature').show() works, because the plugin currently keeps the context around until you exit insert mode, it seems - but I doubt that this behavior is expected / stable?

[debugloop]

Additionally: I use completion.list.selection = "auto_insert" and sometimes I don't accept a result but just continue to type. Signature help does not kick in then either.

E.g. I complete a function call and after selecting I have it inserted as fmt.Printf| (pipe is my cursor). If I just go for a (, making my text fmt.Printf(|), I will not get the signature help either.

[Saghen]

I've wired up show_on_keyword, show_on_insert, and show_on_trigger_character under signature.trigger. You can also open it manually with require('blink.cmp').show_signature()