Feat: Show tabline only when more than one tab

[chrisgrieser]

Requested feature

similar to vim's default behavior, the tabline should only be shown when there is more than one tab. (or there should be an option for that)

Motivation

no reason to "waste" a line when only having one tab.

---

I tried using cond like this, but it seems that "tabs" creates a tabline, even if it is empty.

tabline = {
		lualine_a = {{
			"tabs",
			mode = 1,
			section_separators = "",
			cond = function () return fn.tabpagenr("$") > 1 end,
		}},
	},

[aerosol]

#395 (comment)

[theJian]

I opened a proposal to add a new option for this, @chrisgrieser , let me know what you think.