fix(api): allow nvim_buf_set_extmark to accept end_row key (#16548)

nvim_buf_get_extmark uses "end_row" rather than "end_line" in its
'details' dict, which means callers must modify the key names if they
want to re-use the information. Change the parameter name in
nvim_buf_set_extmark to "end_row" and use "end_line" as an alias
to make this more consistent.

src/nvim/api/keysets.lua

@@ -5,6 +5,7 @@ return {
   set_extmark = {
     "id";
     "end_line";
+    "end_row";
     "end_col";
     "hl_group";
     "virt_text";