vim-patch:8.2.0056: execution stack is incomplete and inefficient

Problem:    Execution stack is incomplete and inefficient.
Solution:   Introduce a proper execution stack and use it instead of
            sourcing_name/sourcing_lnum.  Create a string only when used.
1a47ae32cd

Omit test_debugger.vim: superseded by later patches.
Omit check_map_keycodes(): N/A.
Omit kword_test.c: N/A (converted to a unit test).

src/nvim/lua/executor.c

@@ -1313,6 +1313,7 @@ static void nlua_typval_exec(const char *lcmd, size_t lcmd_len, const char *name
 
 int nlua_source_using_linegetter(LineGetter fgetline, void *cookie, char *name)
 {
+#if 0  // TODO:
   const linenr_T save_sourcing_lnum = sourcing_lnum;
   const sctx_T save_current_sctx = current_sctx;
   current_sctx.sc_sid = SID_STR;
@@ -1336,6 +1337,7 @@ int nlua_source_using_linegetter(LineGetter fgetline, void *cookie, char *name)
   ga_clear_strings(&ga);
   xfree(code);
   return OK;
+#endif
 }
 
 /// Call a LuaCallable given some typvals