[lldb] Add type hints to gdbclientutils.py and fix issues

Everything in this should be python 3.9. The docs say the minimum is 3.8
but there's existing code in this suite that needs 3.9 so I think 3.9 is
ok.

Issues:
qEcho() is passed an argument by the callers that the function didn't have
Several functions in the base class would silently do nothing if not
overriden. These now use @AbstractMethod to require overrides
sendall() had inconsistent return types between overrides

Author: dsandersllvm

lldb/packages/Python/lldbsuite/test/gdbclientutils.py

@@ -6,7 +6,7 @@
 import socket
 import traceback
 from lldbsuite.support import seven
-from typing import Optional, List, Tuple
+from typing import Optional, List, Tuple, Literal
 
 
 def checksum(message):
@@ -520,10 +520,12 @@ class MockGDBServer:
     _receivedData = None
     _receivedDataOffset = None
     _shouldSendAck = True
+    packetLog: list[tuple[Literal["recv"] | Literal["send"], str | bytes]]
 
     def __init__(self, socket):
         self._socket = socket
         self.responder = MockGDBServerResponder()
+        self.packetLog = []
 
     def start(self):
         # Start a thread that waits for a client connection.
@@ -650,11 +652,13 @@ def _parsePacket(self):
         # can start on the next packet the next time around
         self._receivedData = data[i:]
         self._receivedDataOffset = 0
+        self.packetLog.append(("recv", packet))
         return packet
 
     def _sendPacket(self, packet: str):
         assert self._socket is not None
         framed_packet = seven.bitcast_to_bytes(frame_packet(packet))
+        self.packetLog.append(("send", framed_packet))
         self._socket.sendall(framed_packet)
 
     def _handlePacket(self, packet):