[Explore] slice standalone mode doesn't work correctly after refresh browser

[duynguyenhoang]

When going to standalone slice, for example http://localhost:9000/superset/slice/23/?standalone=true
We wil be redirect to http://localhost:9000/superset/explore/?form_data=%7B%22slice_id%22%3A%2023%7D&standalone=true
In explore screen, the url will be replaced by ful form_data. Currenly it doesn't include standalone=true in final url which cause problem when we refresh the browser. It brings us to visualization design screen instead of standalone chart.

Expected results

Standalone slice should be shown when we refresh page http://localhost:9000/superset/slice/23/?standalone=true

Actual results

Visualization design screen is shown.

How to reproduce the bug

1. Go to standalone slice, example http://localhost:9000/superset/slice/23/?standalone=true
2. Waiting it to be rendered fully
3. Refresh browser (F5 or Ctrl R)
4. See the page is now visualization design page, not standalone slice

Environment

(please complete the following information):

• superset version: master
• python version: 3.8
• node.js version: 123

Checklist

Make sure to follow these steps before submitting your issue - thank you!

• I have checked the superset logs for python stacktraces and included it here as text if there are any.
• I have reproduced the issue with at least the latest released version of superset.
• I have checked the issue tracker for the same issue and I haven't found one similar.

[villebro]

Issue fixed by #12359