search: prevent the rendering of the home page when navigating back to the search results

Created by: valerybugakov

Context

TLDR

We render the search home page when navigating back to search results from the blob view. Don't believe me? Go to the cloud instance, set a breakpoint in the SearchPage.tsx file in dev tools and try yourself!

Details

Currently, we have parsedSearchQuery in the state of the SourcegraphWebApp component.

1. Upon opening search results — its value is updated with the current search query.
2. After opening any search result — its value is set to an empty string.
3. When we navigate back to search results we there's a delay in updating its value because:
   • The update is done in the useEffect hook in the Layout component, which is rendered after we figure out which React router route to use. https://github.com/sourcegraph/sourcegraph/blob/ee1e1fe5af79de620292c6794dcbff2c6a47fe71/client/web/src/Layout.tsx#L155-L158
   • It means that the code responsible for deciding what to render doesn't have up-to-date parsedSearchQuery available on the initial render. It leads to rendering the SearchPage component, which we don't need, negatively affecting the perceived performance. https://github.com/sourcegraph/sourcegraph/blob/ee1e1fe5af79de620292c6794dcbff2c6a47fe71/client/web/src/routes.tsx#L78-L82

Changes

• This PR removes parsedSearchQuery from the state of the SourcegraphWebApp component.
  • It seems it's required only in the SourcegraphWebApp componentDidMount hook, and deleting it from the state doesn't break things.
• Uses parsedSearchQuery directly from the Layout component that we already have in place.

As a result — the StreamingSearchResults component is rendered right away when navigating back to search results without redundant intermediate steps.

Preparation to address https://github.com/sourcegraph/sourcegraph/issues/28845.