vim-patch:8.2.4603: sourcing buffer lines is too complicated

Problem:    Sourcing buffer lines is too complicated.
Solution:   Simplify the code. Make it possible to source Vim9 script lines.
            (Yegappan Lakshmanan, closes vim/vim#9974)

85b43c6cb7

This commit changes the behavior of sourcing buffer lines to always have
a script ID, although sourcing the same buffer always produces the same
script ID.

vim-patch:9.1.0372: Calling CLEAR_FIELD() on the same struct twice

Problem:  Calling CLEAR_FIELD() on the same struct twice.
Solution: Remove the second CLEAR_FIELD().  Move the assignment of
          cookie.sourceing_lnum (zeertzjq).

closes: vim/vim#14627

f68517c167

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

test/functional/lua/commands_spec.lua

@@ -207,7 +207,8 @@ describe(':lua', function()
 
     -- ":{range}lua" fails on invalid Lua code.
     eq(
-      [[:{range}lua: Vim(lua):E5107: Error loading lua [string ":{range}lua"]:0: '=' expected near '<eof>']],
+      [[:{range}lua buffer=1: Vim(lua):E5107: Error loading lua ]]
+        .. [[[string ":{range}lua buffer=1"]:0: '=' expected near '<eof>']],
       pcall_err(command, '1lua')
     )