Python: Handle new default for standard library extraction

[yoff]

When you review this, could you also confirm my thinking on the following?

• With the change to feature-flags.ts:
  • Feature.CodeqlActionPythonDefaultIsToNotExtractStdlib will be(come) true iff
    (((the feature flag is on AND NOT the disabling feature flag is on) OR the environment variable is set to true) AND NOT the environment variable is set to false) AND ToolsFeature.PythonDefaultIsToNotExtractStdlib is true.
  • That is, this one entry is enough to make the action react to both the feature flag, the disabling feature flag (x_disabled), and the environment variable. And the tools feature takes precedence, then the environment variable, then the disabling feature flag, then the feature flag.
  • The environment variable "CODEQL_ACTION_DISABLE_PYTHON_STANDARD_LIBRARY_EXTRACTION" is now available to the action.
  • People can write something in their workflow file to turn off the feature.
• With the changes to src/tools-features.ts:
  • ToolsFeature.PythonDefaultIsToNotExtractStdlib is now received from the CLI as long as the entry in there is called
    pythonDefaultIsToNotExtractStdlib
  • if the CLI is not new enough to define this feature, ToolsFeature.PythonDefaultIsToNotExtractStdlib will simply be off.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Confirm the readme has been updated if necessary.
• Confirm the changelog has been updated if necessary.

[tausbn]

Looks good to me! 👍
(However, I'm not familiar with most aspects of how codeql-action works, so we should probably get someone from the core team to give the go-ahead before merging.)

[henrymercer]

LGTM, both on the thinking and the code :)