fix(runtime): fully port emoji_list to Lua

Problem: `runtime/tools/emoji_list.vim` is a Lua script masquerading as
Vimscript, which is unnecessary now that `:source` works for Lua files.

Solution: Remove Vimscript wrapper.

runtime/doc/builtin.txt

@@ -6627,7 +6627,7 @@ setcellwidths({list})                                          *setcellwidths()*
 		To clear the overrides pass an empty {list}: >vim
 		   call setcellwidths([])
 
-<		You can use the script $VIMRUNTIME/tools/emoji_list.vim to see
+<		You can use the script $VIMRUNTIME/tools/emoji_list.lua to see
 		the effect for known emoji characters.  Move the cursor
 		through the text to check if the cell widths of your terminal
 		match with what Vim knows about each emoji.  If it doesn't

runtime/lua/vim/_meta/vimfn.lua

@@ -7904,7 +7904,7 @@ function vim.fn.setbufvar(buf, varname, val) end
 --- To clear the overrides pass an empty {list}: >vim
 ---    call setcellwidths([])
 ---
---- <You can use the script $VIMRUNTIME/tools/emoji_list.vim to see
+--- <You can use the script $VIMRUNTIME/tools/emoji_list.lua to see
 --- the effect for known emoji characters.  Move the cursor
 --- through the text to check if the cell widths of your terminal
 --- match with what Vim knows about each emoji.  If it doesn't

runtime/tools/emoji_list.lua

@@ -0,0 +1,19 @@
+-- Script to fill the window with emoji characters, one per line.
+-- Source this script: :source %
+
+if vim.bo.modified then
+  vim.cmd.new()
+else
+  vim.cmd.enew()
+end
+
+local lnum = 1
+for c = 0x100, 0x1ffff do
+  local cs = vim.fn.nr2char(c)
+  if vim.fn.charclass(cs) == 3 then
+    vim.fn.setline(lnum, string.format('|%s| %d', cs, vim.fn.strwidth(cs)))
+    lnum = lnum + 1
+  end
+end
+
+vim.bo.modified = false

runtime/tools/emoji_list.vim

@@ -1,21 +0,0 @@
-" Script to fill the window with emoji characters, one per line.
-" Source this script: :source %
-
-if &modified
-  new
-else
-  enew
-endif
-
-lua << EOF
-  local lnum = 1
-  for c = 0x100, 0x1ffff do
-    local cs = vim.fn.nr2char(c)
-    if vim.fn.charclass(cs) == 3 then
-      vim.fn.setline(lnum, '|' .. cs .. '| ' .. vim.fn.strwidth(cs))
-      lnum = lnum + 1
-    end
-  end
-EOF
-
-set nomodified

src/nvim/eval.lua

@@ -9464,7 +9464,7 @@ M.funcs = {
       To clear the overrides pass an empty {list}: >vim
          call setcellwidths([])
 
-      <You can use the script $VIMRUNTIME/tools/emoji_list.vim to see
+      <You can use the script $VIMRUNTIME/tools/emoji_list.lua to see
       the effect for known emoji characters.  Move the cursor
       through the text to check if the cell widths of your terminal
       match with what Vim knows about each emoji.  If it doesn't