[EW] Improve EW browse search/replace

Currently we have the preexisting search/replace behaviour on browse. To improve such that: search has clearer separation between pages/find within content; replace option has better separation from central search (ideally available in a separate panel with users having a clear visual of the items being replaced plus a confirm option to avoid destructive operations); revert bulk replace is a possibility.

Source: https://jira.corp.adobe.com/browse/SITES-47729

Start by reviewing the existing browse search/replace behavior and the linked SITES-47729 request. Clarify the separation between page search and in-content search, then define the replacement panel, affected-item preview, confirmation step, and bulk-revert behavior. Done means the workflow is clearly separated and destructive replacements can be reviewed and safely reversed.

Written by the indexing model from the issue text.