[lldb] Add type hints to gdbclientutils.py and use abstract base class (#162172)HEADmain

Everything in this commit should be python 3.8 compatible which has
required using older styles of type hints (e.g. `Optional[T]` rather
than 3.10's `T | None` and `List[T]` rather than 3.9's `list[T]`. There
are some python 3.9 type hints in other files which have not been
changed by this commit.

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

Compatibility was checked with:
```
uvx vermin -t 3.8 $(find lldb/packages/Python -name '*.py')
```
Compability of the type hints was checked with:
```
uvx vermin -t 3.8 --eval-annotations $(find lldb/packages/Python -name '*.py')
```
and type hint correctness was checked with
```
uvx pyright lldb/packages/Python/lldbsuite/test/gdbclientutils.py
```

0 files changed, 0 insertions, 0 deletions