feat: allow :wincmd to accept a count

Lets the `:wincmd` command accept a count like its documentation suggests, previously it could only accept a range, which lead to some ambiguity on which attribute should be used when executing `wincmd` using `nvim_cmd`.

Closes #19662.

Also fixes a typo in a related Vim test which should be fixed in Vim by vim/vim#10932.

runtime/doc/windows.txt

@@ -442,6 +442,7 @@ position is set to keep the same Visual area selected.
 These commands can also be executed with ":wincmd":
 
 :[count]winc[md] {arg}
+:winc[md] [count] {arg}
 		Like executing CTRL-W [count] {arg}.  Example: >
 			:wincmd j
 <		Moves to the window below the current one.

src/nvim/ex_cmds.lua

@@ -3181,7 +3181,7 @@ module.cmds = {
   },
   {
     command='wincmd',
-    flags=bit.bor(NEEDARG, WORD1, RANGE, CMDWIN, LOCK_OK),
+    flags=bit.bor(NEEDARG, WORD1, RANGE, COUNT, CMDWIN, LOCK_OK),
     addr_type='ADDR_OTHER',
     func='ex_wincmd',
   },

src/nvim/testdir/test_diffmode.vim

@@ -137,7 +137,7 @@ func Common_vert_split()
 
   " Test diffoff
   diffoff!
-  1wincmd 2
+  1wincmd w
   let &diff = 1
   let &fdm = diff_fdm
   let &fdc = diff_fdc

test/functional/ex_cmds/wincmd_spec.lua

@@ -0,0 +1,12 @@
+local helpers = require("test.functional.helpers")(after_each)
+local clear = helpers.clear
+local eq = helpers.eq
+local meths = helpers.meths
+local command = helpers.command
+
+it(':wincmd accepts a count', function()
+  clear()
+  command('vsplit')
+  command('wincmd 2 w')
+  eq(meths.get_current_win().id, 1000)
+end)