feat(layout_config) Adds the option to configure additional lines of padding around the anchor of the layout (#2851)

[Weyaaron]

Description

This PR adds a new option to layout_config called anchor_padding. When set to a positive integer, it adds
additional lines of padding around the anchor of a layout.

Fixes #2851

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Test for anchor south and with high padding:

local telescope = require("telescope")

local vertical_config = {
	config = {
		vertical = { width = 0.5 },
		anchor = "S",
		prompt_position = "bottom",
		width = { padding = 0 },
		height = 0.5,
		anchor_padding = 10,
	},
}
telescope.setup({
	pickers = {},
	extensions = {},
	defaults =config,
})

This results in the following layout:

The result we care about is the ten lines of additional space between the bottom of the screen and the start of the layout.

• Test for anchor north and with low padding:

local telescope = require("telescope")
local config = {
	layout_config = {
		vertical = { width = 0.5 },
		anchor = "N",
		prompt_position = "bottom",
		width = { padding = 0 },
		height = 0.5,
		anchor_padding = 2,
	},
}
telescope.setup({
	pickers = {},
	extensions = {},
	defaults =config,
})

This results in the following layout:

The result we care about is the two lines of additional space between the top of the screen and the start of the layout.

Configuration:

• Neovim version (nvim --version): v0.9.4
• Operating system and version:
  OS: Manjaro Linux x86_64
  Host: Laptop (12th Gen Intel Core) A4
  Kernel: 6.1.80-1-MANJARO

Checklist:

• My code follows the style guidelines of this project (stylua)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (lua annotations)

I am not quite sure what this last point is about, so I left it open.

Open question:

I have not provided additional tests. I have changed the existing tests to mimic the previous behavior by setting anchorpadding to 1 where applicable. Since this is my first contribution, I am unsure about this. Additional feedback is appreciated.