[lldb-dap] NFC Renaming files for consistency. (#178560)

I noticed recently that CompletionsHandler.cpp and
BreakpointLocationsHandler.cpp do not follow the same naming pattern as
the rest of the request handlers.

Renaming to include `Request` for consistency.

GitOrigin-RevId: 1f8058ec64a69443f5ce2373557eff1c4d877010
3 files changed