Factor out stack_trace dependency

It would be really helpful if the test package did not have the dependency on the stack_trace package, and either just used VM stacks unmodified or had some hook you could provide to decide how to handle stack traces. Right now, in Flutter, we try to catch all the stack traces but some get caught by the test framework and this then mangles the output of our error handling logic (which is expecting raw stack traces from the VM).

We unfortunately can't rely on the vmTrace property because to use that we'd have to import stack_trace at the framework level, and we would like to minimise our dependencies.

No files, tests, or entry points are named. Start by tracing where the test package imports and processes stack_trace, then review how Flutter captures raw VM stacks. Done means the dependency is removed or a clear hook allows callers to preserve the stack-trace representation they need.

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