feat(defaults): dot-repeat [<Space> #31186

Problem: `[<Space>` and `]<Space>` do not support repetition.

Solution: use `operatorfunc` and `g@l` to make these mappings dot
repeatable.

runtime/lua/vim/_buf.lua

@@ -0,0 +1,23 @@
+local M = {}
+
+--- Adds one or more blank lines above or below the cursor.
+-- TODO: move to _defaults.lua once it is possible to assign a Lua function to options #25672
+--- @param above? boolean Place blank line(s) above the cursor
+local function add_blank(above)
+  local offset = above and 1 or 0
+  local repeated = vim.fn['repeat']({ '' }, vim.v.count1)
+  local linenr = vim.api.nvim_win_get_cursor(0)[1]
+  vim.api.nvim_buf_set_lines(0, linenr - offset, linenr - offset, true, repeated)
+end
+
+-- TODO: move to _defaults.lua once it is possible to assign a Lua function to options #25672
+function M.space_above()
+  add_blank(true)
+end
+
+-- TODO: move to _defaults.lua once it is possible to assign a Lua function to options #25672
+function M.space_below()
+  add_blank()
+end
+
+return M