Use custom popup menu

What's Changed

Break changes

• Use custom popup menu instead of vim's built-in pum, see :h coc-completion or #3862
  • Minimal version changed to nvim >= 0.4.0 and vim >= 8.1.1719.
  • Removed configurations: suggest.enablePreview suggest.keepCompleteopt suggest.disableKind suggest.disableMenu suggest.floatEnable suggest.disableMenuShortcut.
  • "suggest.noselect" changed to false by default, like VSCode.
  • "suggest.enablePreselect" changed to true by default, like VSCode.
  • Add "suggest.formatItems" for customize layout in popupmenu.
  • Need to remap keys to manage completion list.
• Remove configuration list.matchHighlightGroup, use highlight group CocListSearch for matched characters.
• Always use picker to message with actions, remove configuration notification.preferMenuPicker
• Disable progressOnInitialization for language client by default.
• Support repeat#set for commands that make changes only.

New features

• Add configuration "notification.disabledProgressSources".
• Add "rounded" property to "floatConfig" configuration.
• Add configuration workspace.openOutputCommand.

Full Changelog: 540b286...7a50d4d