Allow setting a survey to only show up on mobile web, not on mobile native

Feature request

Is your feature request related to a problem?

Currently, I'm able to filter a survey so it only shows up on certain device types, which are Desktop/Tablet/Mobile.

However, if I do not want to have a survey show up on native mobile, there's no clear path.

Describe the solution you'd like

I'd like to differentiate between mobile web (browser / webview) and mobile native, to set a survey to only show on either of these cases.

Describe alternatives you've considered

A workaround is setting a survey to be shown only after an event is captured only on the web (like $pageview).

Debug info

- [ ] PostHog Cloud, Debug information: [please copy/paste from https://us.posthog.com/settings/project-details#variables]
- [ ] PostHog Hobby self-hosted with `docker compose`, version/commit: [please provide]
- [ ] PostHog self-hosted with Kubernetes (deprecated, see [`Sunsetting Kubernetes support`](https://posthog.com/blog/sunsetting-helm-support-posthog)), version/commit: [please provide]

No files, tests, or entry points are named. Trace the existing survey device-type filtering, then identify where mobile web and native mobile contexts are distinguished. Done means a survey can target mobile web separately from native mobile while preserving the existing Desktop, Tablet, and Mobile options.