refactor(gen_api_dispatch): avoid trailing spaces (#32632)

Problem:
Generated Lua API bindings may have trailing spaces (e.g. nvim_set_hl).

Solution:
Add leading spaces only if arg_free_code is non-empty.
Also:
- Remove an unnecessary string.format() in write_shifted_output() args.
- Fix incorrect indent for the nlua_push_keydict() below.

src/nvim/generators/gen_api_dispatch.lua

@@ -791,12 +791,12 @@ local function process_function(fn)
     local arg_free_code = ''
     if param[1] == 'Object' then
       extra = 'true, '
-      arg_free_code = 'api_luarefs_free_object(' .. cparam .. ');'
+      arg_free_code = '  api_luarefs_free_object(' .. cparam .. ');'
     elseif param[1] == 'DictOf(LuaRef)' then
       extra = 'true, '
-      arg_free_code = 'api_luarefs_free_dict(' .. cparam .. ');'
+      arg_free_code = '  api_luarefs_free_dict(' .. cparam .. ');'
     elseif param[1] == 'LuaRef' then
-      arg_free_code = 'api_free_luaref(' .. cparam .. ');'
+      arg_free_code = '  api_free_luaref(' .. cparam .. ');'
     end
     local errshift = 0
     local seterr = ''
@@ -813,7 +813,7 @@ local function process_function(fn)
       )
       cparam = '&' .. cparam
       errshift = 1 -- free incomplete dict on error
-      arg_free_code = 'api_luarefs_free_keydict('
+      arg_free_code = '  api_luarefs_free_keydict('
         .. cparam
         .. ', '
         .. string.sub(param_type, 9)
@@ -862,9 +862,9 @@ local function process_function(fn)
     local rev_i = #free_code - i + 1
     local code = free_code[rev_i]
     if i == 1 and not string.match(real_type(fn.parameters[1][1]), '^KeyDict_') then
-      free_at_exit_code = free_at_exit_code .. ('\n  %s'):format(code)
+      free_at_exit_code = free_at_exit_code .. ('\n%s'):format(code)
     else
-      free_at_exit_code = free_at_exit_code .. ('\nexit_%u:\n  %s'):format(rev_i, code)
+      free_at_exit_code = free_at_exit_code .. ('\nexit_%u:\n%s'):format(rev_i, code)
     end
   end
   local err_throw_code = [[
@@ -901,7 +901,7 @@ exit_0:
     local ret_mode = (ret_type == 'Object') and '&' or ''
     if fn.has_lua_imp then
       -- only push onto the Lua stack if we haven't already
-      write_shifted_output(string.format(
+      write_shifted_output(
         [[
     if (lua_gettop(lstate) == 0) {
       nlua_push_%s(lstate, %sret, kNluaPushSpecial | kNluaPushFreeRefs);
@@ -909,10 +909,10 @@ exit_0:
       ]],
         return_type,
         ret_mode
-      ))
+      )
     elseif string.match(ret_type, '^KeyDict_') then
       write_shifted_output(
-        '     nlua_push_keydict(lstate, &ret, %s_table);\n',
+        '    nlua_push_keydict(lstate, &ret, %s_table);\n',
         string.sub(ret_type, 9)
       )
     else
@@ -927,7 +927,6 @@ exit_0:
 
     -- NOTE: we currently assume err_throw needs nothing from arena
     write_shifted_output(
-
       [[
   %s
   %s