When open search, should lock the scroll bar to avoid page jitter

## Description
windows + chrome. When open search, should lock the scroll bar to avoid page jitter

should like
1. https://anu-vue.netlify.app/guide/components/dialog.html click dialog btn
2. https://vuetifyjs.com/en/components/dialogs/ click dialog btn

## Steps to reproduce

1. open "https://docsearch.algolia.com/"， has scrollbar
3. Click search
4. page scroll bar hide
5. Page jitter

## Expected behavior

## Environment

- OS: [e.g. Windows / Linux / macOS / iOS / Android]
- Browser: [e.g. Chrome, Safari]
- DocSearch version: [e.g. 3.0.0]

Reproduce the issue on docsearch.algolia.com in Windows Chrome by opening search and observing the page scrollbar and resulting jitter. Trace the search-opening UI and determine how scrollbar locking is handled; done means opening search no longer shifts the page while the scrollbar is hidden.

Written by the indexing model from the issue text.