[lldb/Reproducers] Decode run-length encoding in GDB replay server.

The GDB replay server sanity-checks that every packet it receives
matches what it expects from the serialized packet log. This mechanism
tripped for TestReproducerAttach.py on Linux, because one of the packets
(jModulesInfo) uses run-length encoding. The replay server was comparing
the expanded incoming packet with the unexpanded packet in the log. As a
result, it claimed to have received an unexpected packet, which caused
the test to fail.

This patch addresses that issue by expanding the run-length encoding
before comparing the packets.

Differential revision: https://reviews.llvm.org/D76163