In https://github.com/llvm/llvm-project/pull/170523 it was pointed out
that the spec does specifically specify that launch/attach should not
respond until configurationDone is handled.
This means we do need to support async request handlers. To better align
with the spec, I've added a new `lldb_dap::AsyncRequestHandler`. This is
an additional handler type that allows us to respond at a later point.
Additionally, I refactored `launch` and `attach` to only respond once
the `configurationDone` is complete, specifically during the `PostRun`
operation of the `configurationDone` handler.
I merged some of the common behavior between `RequestHandler` and
`AsyncRequestHandler` into their common `BaseRequestHandler`.
The flow should now be:
```
<-> initialize request / response
--> launch/attach request
<-- event initialized
... optionally ...
<-> setBreakpoints request / response
<-> setFunctionBreakpoints request / response
<-> setExceptionBreakpoints request / response
<-> setInstructionBreakpoints request / response
... finally ...
<-> configurationDone request / response
<-- launch/attach response
```
---------
Co-authored-by: Jonas Devlieghere <jonas@devlieghere.com>
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