Grouping - Improve grouping when there is an UI thread and Game thread

### Problem Statement

Currently we don't display of Java + Native stacktrace nicely. https://github.com/getsentry/sentry/issues/103299
But another issue is that the grouping is only based on the Java stacktrace.
What happens is that there are ANR's grouped by main (UI) thread stacktraces but it would be usefull to have the option to subdivide them by mainLoop() game thread as it's often pointing to the real problem.

I tried to check if it can be done clientside but:
"I don't think this kind of thing can in general be done at client-side. An ANR is often the result of a deadlock, and analysing the root cause of a deadlock is not trivial. At best we can come up with heuristics for some specific issues we encounter, but because they are so situation-dependent, they should be configurable at server-side.

That being said, if we have to blindly select a single thread for grouping, choosing the game thread would typically be much more useful than choosing the UI thread."

See example issues in Linear ticket

### Solution Brainstorm

Have the option to depend on the game thread

### Product Area

Issues

Start with the problem statement and the linked Sentry issue 103299, then review the example issues referenced in the Linear ticket. The proposed direction is to support server-side grouping that can use the game thread rather than only the UI thread, but no files, tests, or concrete acceptance criteria are named.

Written by the indexing model from the issue text.