backport: docs: misc, window (#39722)

- formalize `window-number` similar to `tabpage-number`.
- reference it from docs.

runtime/lua/vim/_meta/options.gen.lua

@@ -6808,7 +6808,7 @@ vim.wo.stc = vim.wo.statuscolumn
 ---          added without modifying code that reacts on mouse clicks on
 ---          this label.
 ---       Use `getmousepos()`.winid in the specified function to get the
----       corresponding window id of the clicked item.
+---       corresponding `window-ID` of the clicked item.
 --- \< -   Where to truncate line if too long.  Default is at the start.
 ---       No width fields allowed.
 --- = -   Separation point between alignment sections.  Each section will
@@ -7517,12 +7517,20 @@ vim.o.ttm = vim.o.ttimeoutlen
 vim.go.ttimeoutlen = vim.o.ttimeoutlen
 vim.go.ttm = vim.go.ttimeoutlen
 
---- Assume that the underlying terminal can respond quickly to queries
---- required by features such as 'background' detection.
+--- Enables Nvim `TUI` features which assume a fast (usually local) host
+--- terminal. During startup, Nvim queries the terminal (for 'background'
+--- detection, etc.) and must wait for a response (or timeout).
 ---
---- Nvim issues terminal queries before reading the user's `config` file,
---- so disabling this option there will not work. Set $NVIM_NOTTYFAST
---- before starting Nvim to disable terminal queries.
+--- If your terminal environment is slow (e.g. remote SSH), or broken
+--- (doesn't respond to queries), Nvim startup may be slower. Therefore
+--- you can disable this option by setting the `$NVIM_NOTTYFAST`
+--- environment variable before starting Nvim:
+--- ```
+--- 	NVIM_NOTTYFAST=1 nvim
+--- ```
+---
+--- The queries are performed early, before `--cmd` and user `config`, so
+--- `:set nottyfast` in your config happens too late.
 ---
 --- @type boolean
 vim.o.ttyfast = true