Add experiment support to debug configuration caching

[karthiknadig]

No description provided.

[karthiknadig]

Verification steps:

1. Make sure you have "python.experiments.optInto": ["All"], in your user settings. If you did not have it, add it and reload.
2. Make sure you don't have any launch.json files under or any launch configurations.
3. Create a python file in vscode. Use following content if you need:

import math

SQ5 = math.sqrt(5.0)


def fib(n):
    # Compute nth Fibonacci number without recursion
    return math.floor((((1.0 + SQ5) ** n) - ((1.0 - SQ5) ** n)) / (SQ5 * (2 ** n)))


print(fib(10))

4. Set breakpoint any where in file, and start debugging.
5. You will be asked to select one of the pre-defined debug configurations, Select current file.
6. You should hit a breakpoint. End the debugging session and start debugging again.
7. This time you should not be asked to select a debug configuration.

[weinand]

That works fine (after switching to the Insider version of Python extension...)