Session Replay masking of WebView content

### Problem Statement

I've got Android and iOS applications that have a lot of native screens and also heavily use WebView to display webpages from my domain. Right now Session Replay doesn't support masking only chosen parts of the WebView - either the whole view is masked or nothing at all. Neither option works for me because with the whole WebView greyed out it doesn't add any value, but I cannot unmask everything due to security reasons.
I'd be great to have a greater control in this workflow. I'm using Sentry for both Mobile and Frontend projects if it helps at all with creating a solution.

### Solution Brainstorm

_No response_

No files, tests, or entry points are identified. Start by reviewing how Session Replay masking is handled for Android and iOS WebView content; done would require an agreed implementation that masks selected WebView regions while preserving permitted content.

Written by the indexing model from the issue text.