feat: add textobjects.scm

[mrdgo]

This PR implements the first queries for #119.

With this sample config, you can hit yaf (yank around function) to copy the closest function, dif (delete in function) to clear the contet of the closest function, with sourround-like plugins ysaSb (sourround around "()"-block) to sourround a statement with parentheses, or whatever keys you map to what query.

textobjects = {
    select = {
        enable = true,
        keymaps = {
            -- You can use the capture groups defined in textobjects.scm
            -- For example:
            -- Nushell only
            ["aP"] = "@pipeline.outer",
            ["iP"] = "@pipeline.inner", -- selects the closest pipeline element

            -- supported in other languages as well
            ["af"] = "@function.outer",
            ["if"] = "@function.inner",
            ["al"] = "@loop.outer",
            ["il"] = "@loop.inner",
            ["aC"] = "@conditional.outer",
            ["iC"] = "@conditional.inner",
            ["iS"] = "@statement.inner",
            ["aS"] = "@statement.outer",
        }, -- keymaps
    }, -- select
}, -- textobjects

To me, these queries are sufficient. I wouldn't setup any other ones, so I'd declare this as ready to merge. Feel free to request additional queries.

[fdncred]

Looks fun! Thanks!