fix(editor): respect [+cmd] when executing :drop #33339

Problem:
Normally, `:drop +41 foo.txt` will open foo.txt with the cursor on line
41. But if foo.txt is already open, it instead is a no-op, even if the
cursor is on a different line.

Steps to reproduce:

    nvim --clean foo.txt
    :drop +30 foo.txt

Solution:
Handle +cmd in ex_drop().

1 files changed, 21 insertions, 0 deletions

diff --git a/test/functional/ex_cmds/drop_spec.lua b/test/functional/ex_cmds/drop_spec.lua
index d341c823b9..cd1ca978aa 100644
--- a/test/functional/ex_cmds/drop_spec.lua
+++ b/test/functional/ex_cmds/drop_spec.lua
@@ -75,4 +75,25 @@ describe(':drop', function()
       :drop Xdrop_modified.txt           |
     ]])
   end)
+
+  it('jumps to line number when passed +line', function()
+    exec([[
+      edit Xdrop_line.txt
+      call append(0, "I just miss doing art. Don't you?")
+      call append(1, "It is not so hard as we have supposed.")
+      call append(2, "We are propelled by disaster. We are moving swiftly.")
+    ]])
+    feed_command('drop +2 Xdrop_line.txt')
+    screen:expect([[
+      I just miss doing art. Don't you?  |
+      ^It is not so hard as we have suppos|
+      ed.                                |
+      We are propelled by disaster. We ar|
+      e moving swiftly.                  |
+                                         |
+      {0:~                                  }|*2
+      {1:Xdrop_line.txt [+]                 }|
+      :drop +2 Xdrop_line.txt            |
+    ]])
+  end)
 end)