fix(:restart): reuse --listen addr on Windows #38539

Problem:
On Windows, :restart cannot immediately reuse the canonical --listen
address because named pipe release is asynchronous.

Solution:
Start the new Nvim server on a temporary address; in the new Nvim,
retry serverstart() with the original ("canonical") address until it
succeeds.

test/functional/core/main_spec.lua

@@ -216,7 +216,10 @@ describe('vim._core', function()
     t.matches("^module 'vim%.hl' not found:", t.pcall_err(n.exec_lua, [[require('vim.hl')]]))
 
     -- All `vim._core.*` modules are builtin.
-    t.eq({ 'serverlist' }, n.exec_lua([[return vim.tbl_keys(require('vim._core.server'))]]))
+    t.eq(
+      { 'rebind_old_addr_after_restart', 'serverlist' },
+      n.exec_lua([[local k = vim.tbl_keys(require('vim._core.server')); table.sort(k); return k]])
+    )
     local expected = {
       'vim.F',
       'vim._core.defaults',