fix(api): generic error messages, not using TRY_WRAP #31596

Problem:
- API functions using `try_start` directly, do not surface the
  underlying error message, and instead show generic messages.
- Error-handling code is duplicated in the API impl.
- Failure modes are not tested.

Solution:
- Use `TRY_WRAP`.
- Add tests.

test/functional/api/window_spec.lua

@@ -359,6 +359,15 @@ describe('API/win', function()
       eq(2, api.nvim_win_get_height(api.nvim_list_wins()[2]))
     end)
 
+    it('failure modes', function()
+      command('split')
+      eq('Invalid window id: 999999', pcall_err(api.nvim_win_set_height, 999999, 10))
+      eq(
+        'Wrong type for argument 2 when calling nvim_win_set_height, expecting Integer',
+        pcall_err(api.nvim_win_set_height, 0, 0.9)
+      )
+    end)
+
     it('correctly handles height=1', function()
       command('split')
       api.nvim_set_current_win(api.nvim_list_wins()[1])
@@ -409,6 +418,15 @@ describe('API/win', function()
       eq(2, api.nvim_win_get_width(api.nvim_list_wins()[2]))
     end)
 
+    it('failure modes', function()
+      command('vsplit')
+      eq('Invalid window id: 999999', pcall_err(api.nvim_win_set_width, 999999, 10))
+      eq(
+        'Wrong type for argument 2 when calling nvim_win_set_width, expecting Integer',
+        pcall_err(api.nvim_win_set_width, 0, 0.9)
+      )
+    end)
+
     it('do not cause ml_get errors with foldmethod=expr #19989', function()
       insert([[
         aaaaa