Do not close documentation while completing in insert mode

[ChrisAmelia]

This is related to https://github.com/neoclide/coc.nvim/issues/2102

This seems to happen only with Java so far, tested with Go completion and it works as expected. Can be reproduced with these minimal configs:

init.vim

set runtimepath^=~/.local/share/nvim/plugged/coc.nvim
filetype plugin indent on
syntax on
set hidden

augroup mygroup
  " Update signature help on jump placeholder.
  autocmd User CocJumpPlaceholder call CocActionAsync('showSignatureHelp')
augroup end

coc-settings.json

"java.signatureHelp.enabled": true

To reproduce

1. Create a file Main.java with:

public class Main {

    public static void main(String[] args) {
        String word = "Hello, World";
    }
}

2. Complete word with method startsWith(String prefix, int offset):

public class Main {

    public static void main(String[] args) {
        String word = "Hello, World";
        word.startsWith(
    }
}

Cursor is now positioned on the first parameter with documentation shown, as expected.
Press any key, while in insert mode, and documentation disappears.