This patch updates the `lldbutil.fetch_next_event` helper function to
either match a specific broadcaster or match a whole broadcaster class.
This is very handy when testing process events for interactive scripted
process debugging.
This also fixes a bug in the failing case, where `SBEvent.GetDescription`
expects a `SBStream` argument. We never took that code path in the
original implementation so we didn't hit that bug.
Differential Revision: https://reviews.llvm.org/D149175
Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>
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