Visual studio completions don't support variables in the edit text

[rchiodo]

Open the file here:
https://github.com/microsoft/pylance-release/blob/main/testing/single/src/completion.py

Run the last example, that is trying to add completions for the __init__ method.

Expected result:

# bring up override completion after `__init__` and confirm `__init__` is suggested
# commit the completion and confirm the generated code. also verify undo work.
class BuiltInMethod:
    def __init__(self) -> None:
        pass

Actual result:

# bring up override completion after `__init__` and confirm `__init__` is suggested
# commit the completion and confirm the generated code. also verify undo work.
class BuiltInMethod:
    def __init__(self) -> None:
    ${0:pass}

[StellaHuang95]

VS Client doesn't currently support the snippetSupport capability, but I enabled it by hardcoding pylance to the list of servers that enable experimental snippet support. Not sure why it's not working, needs further investigation.