feat(lspsaga): support v0.2.7

[Jint-lzxy]

This PR added support for lspsaga@v0.2.7. Changes include:

• Implemented new highlight groups;
• The LspKind* highlight groups are used to set the colors for lspkind icons (finally!)
  • Note: Those highlights do not belong to any integration. I added them to support "dynamically changing flavors when editing". Not sure if this is the best way to do so.

It'll be marked as ready for review after changes are merged upstream 👍

[nullchilly]

In favour of directly using SagaWinbarClass = { link = "Class } instead of custom_kind because lspsaga makes no effect to preserve highlight groups on ColorScheme event

[Jint-lzxy]

In favour of directly using SagaWinbarClass = { link = "Class } instead of custom_kind because lspsaga makes no effect to preserve highlight groups on ColorScheme event

@nullchilly Sorry, I can't quite understand that. Now lspsaga uses highlight groups to which the lspkind icons are linked to set all its colors. If we only set highlights for winbar, the icons for other features (such as outline) will have no color then. IMO lspsaga can handle this correctly now, see: lspkind.lua#L110.

Did I miss something here?