In the script that's used by RPC to convert LLDB headers to LLDB RPC
headers, there's a bug with how it converts namespace usage. An
overeager regex pattern caused *all* text before any `lldb::` namespace
usage to get replaced with `lldb_rpc::` instead of just the namespace
itself. This commit changes that regex pattern to be less overeager and
modifies one of the shell tests for this script to actually check that
the namespace usage replacement is working correctly.
rdar://154126268
92a7f6fbbe