[llvm] [Dexter] Replace DAP "initialized" timeout with a warning (PR #174198)

[Stephen Tozer via llvm-commits]

SLTozer wrote:

> So the consequence of this would be that the tests just take longer to launch in some cases?

Not as a result of this patch directly; the timeout is simply how long Dexter will wait before printing a warning, rather than a fixed delay. But if the startup sequence is taking more than 3 seconds, I'd say that does seem like the tests are quite slow; shouldn't be a problem though since there aren't very many of them. I don't we can conclusively say the launch time has increased recently either; to summarize the recent changes to Dexter/LLDB:

1. https://github.com/llvm/llvm-project/pull/163653 modified the LLDB launch sequence logic, which also led to Dexter tests failing as it expected a difference sequence.
2. https://github.com/llvm/llvm-project/pull/169744 modified Dexter's launch sequencing to make it compatible with LLDB, but also broke it's compatibility with other debuggers (and the DAP specification).
3. #170523 modified Dexter's launch sequencing again to make it compatible with both LLDB and the DAP spec, and at the same time added the `initialized` event timeout.
4. https://github.com/llvm/llvm-project/pull/171549 modified LLDB's launch sequencing to be compatible with the DAP spec - no corresponding changes to Dexter required, since they now both follow the spec faithfully.

Since the timeout was only added in change (3), and it also appears to have been getting hit on the bots from the start, it's unclear whether it was always taking this long to start, or if that is a recent change; we can only conclusively say that change (4) is not (solely) responsible since the timeout was getting hit before it landed.

https://github.com/llvm/llvm-project/pull/174198