feat(cwd)!: :lcd! (bang), rearrange :bcd/:lcd/… scope precedence #41194

Problem:
- buf-local CWD scope is lower priority than :lcd, which is weird.
  ```
  win > buf > tab > global
  ```
- No way to clear current CWD at a given scope.

Solution:
- Rerrange scope precedence to:
  ```
  buf > win > tab > global
  ```
- Introduce "bang" variants (`:bcd!`/`:lcd!`/`:tcd!`) which clears the
  local CWD for the given scope.

runtime/lua/vim/_meta/vimfn.gen.lua

@@ -947,30 +947,22 @@ function vim.fn.charcol(expr, winid) end
 --- @return integer
 function vim.fn.charidx(string, idx, countcc, utf16) end
 
---- Lua: Prefer |nvim_set_current_dir()| for the global directory; tab-local, window-local, and return semantics differ.
+--- Sets the |current-directory| of the given {scope}:
+---     - "buffer"    Changes the buffer-local directory.  |:bcd|
+---     - "window"    Changes the window-local directory.  |:lcd|
+---     - "tabpage"   Changes the tabpage-local directory.  |:tcd|
+---     - "global"    Changes the global directory.  |:cd|
 ---
---- Changes the current working directory to {dir}.  The scope of
---- the change is determined as follows:
---- If {scope} is not present, the current working directory is
---- changed to the scope of the current directory:
----     - If the window local directory (|:lcd|) is set, it
----       changes the current working directory for that scope.
----     - If the buffer local directory (|:bcd|) is set, it
----       changes the current working directory for that scope.
----     - Otherwise, if the tabpage local directory (|:tcd|) is
----       set, it changes the current directory for that scope.
----     - Otherwise, changes the global directory for that scope.
+--- If {scope} is not given it is decided as follows:
+---     - If buffer-local directory (|:bcd|) is set, scope is
+---       "buffer".
+---     - If the window-local directory (|:lcd|) is set, scope is
+---       "window".
+---     - If the tabpage-local directory (|:tcd|) is set, scope is
+---       "tabpage".
+---     - Otherwise, scope is "global".
 ---
---- If {scope} is present, changes the current working directory
---- for the specified scope:
----     "buffer"  Changes the buffer local directory.  |:bcd|
----     "window"  Changes the window local directory.  |:lcd|
----     "tabpage"  Changes the tabpage local directory.  |:tcd|
----     "global"  Changes the global directory.  |:cd|
----
---- {dir} must be a String.
---- If successful, returns the previous working directory.  Pass
---- this to another chdir() to restore the directory.
+--- If successful, returns the previous working directory.
 --- On failure, returns an empty string.
 ---
 --- Example: >vim
@@ -3321,41 +3313,37 @@ function vim.fn.getcurpos(winid) end
 --- @return any
 function vim.fn.getcursorcharpos(winid) end
 
---- Lua: Prefer |uv.cwd()| for the global working directory; tab-local and window-local scopes differ.
+--- Without arguments, returns the effective |current-directory|.
+--- With {winnr} (|window-number| or |window-ID|), {tabnr} or
+--- {bufnr} the working directory of that scope is returned,
+--- ignoring 'autochdir'.
 ---
---- With no arguments, returns the name of the effective
---- |current-directory|. With {winnr} or {tabnr} or {bufnr} the
---- working directory of that scope is returned, and 'autochdir'
---- is ignored.
+--- - If {winnr} is -1: gets the tabpage directory.
+--- - If {winnr} and {tabnr} are both -1: gets the global
+---   directory.
+---   - Note: Vim returns an empty string when {tabnr} is -1.
+--- - If {bufnr} is given: gets the buffer-local directory.
+---   ({winnr} and {tabnr} must be -1.)
+--- - An argument may be -1 only if preceding args are -1. *E5001*
 ---
 --- Tabs, windows and buffers are identified by their respective
 --- numbers, 0 means current tab/window/buffer. Missing {tabnr}
 --- implies 0 (missing {bufnr} does not; see below). Thus the
 --- following are equivalent: >vim
----   getcwd(0)
----   getcwd(0, 0)
---- <If {winnr} is -1 it is ignored, only the tab is resolved.
---- {winnr} is a |window-number| or |window-ID|.
+---     getcwd(0)
+---     getcwd(0, 0)
+--- <
+--- Each form reports its own scope or "wider", so e.g. {winnr}
+--- never reports a buffer-local directory.  The {bufnr} form
+--- falls back to the global directory, because a buffer belongs
+--- to no particular window or tabpage.
 ---
---- If both {winnr} and {tabnr} are -1 and {bufnr} is missing the
---- global working directory is returned.
----
---- Note: When {tabnr} is -1 Vim returns an empty string to
---- signal that it is invalid, whereas Nvim returns either the
---- global working directory if {winnr} is -1 or the working
---- directory of the window indicated by {winnr}.
----
---- If {bufnr} is provided, {winnr} and {tabnr} must be -1, then
---- the buffer-local working directory is returned.
----
---- An argument may be -1 only if all preceding arguments are -1.
----
---- Examples of buffer usage: >vim
+--- Examples: >vim
 ---       getcwd(-1, -1, 0)  " Get current buffer's directory
----       getcwd(-1, -1, 3)  " Get directory of buffer #3
+---       getcwd(-1, -1, 3)  " Get directory of buffer 3
 ---       getcwd(-1, -1, -1) " Get global directory
 ---       getcwd(-1, -1)     " Get global directory
---- <Throw error if the arguments are invalid.
+--- <
 ---
 --- @param winnr? integer
 --- @param tabnr? integer