[Feature] Improve Path:normalize to return shorter relative path using ../

[powerman]

Currently Path:normalize returns 3 possible paths:

• absolute from /
• absolute from ~
• relative down from cwd

I propose to add a fourth one:

• relative up from cwd

At a glance this changes behaviour in a compatible way and shouldn't break any uses.

The point is to get the shortest possible path (which is anyway feels like a current goal for this method) - sometimes it may be the absolute one, sometimes up from cwd.

I've found it really useful in Neovim, when file is opened using Telescope plugin and you doesn't control how file name will be formed (manually you can either do :tabnew ../file or :tabnew ~/proj/file), but you wanna see as short as possible file name in statusline/tab name. Here is my current implementation (as a Lazy plugin):

---@type LazySpec
return {
    {
        'nvim-lua/plenary.nvim', -- Not a plugin, just a useful library.
        config = function()
            local Path = require 'plenary.path'

            local normalize = Path.normalize
            --- Monkey-patch Path:normalize method to make it try harder looking for shortest
            --- relative path by checking also path UP from cwd: '../../…'.
            ---@diagnostic disable-next-line: duplicate-set-field
            Path.normalize = function(self, cwd)
                -- Absolute (DOWN FROM / or ~) or relative (DOWN FROM cwd).
                local orig = normalize(self, cwd)
                -- Absolute (DOWN FROM / or ~), but we'll make it relative (UP FROM cwd).
                local rel = vim.fn.fnamemodify(orig, ':p:~')

                if string.match(orig, '^[/~]') then -- Absolute, thus may be shorter.
                    local abs = vim.fn.fnamemodify(rel, ':p')
                    local abs_path = Path:new(abs)
                    local dir = cwd .. '/'
                    local up = ''
                    repeat
                        up = up .. '../'
                        rel = abs_path:make_relative(Path:new(dir .. up):absolute())
                    until rel ~= abs
                    rel = up .. rel
                end

                return string.len(orig) <= string.len(rel) and orig or rel
            end
        end,
    },
}

This implementation is not suitable for the lib (because there is no Windows support and it depends on Neovim), but sometimes code worth thousands words 😄 and also it may be useful for other Neovim users until this change will be implemented (if it will be accepted at all).