Default python.useEnvironmentsExtension to true for all users #1908

Need: Users who have telemetry disabled cannot be enrolled in the experiment that enables the Python Environments extension, so they remain on the legacy environment experience. Defaulting python.useEnvironmentsExtension to true ensures those users also move to the Python Environments extension.

This issue tracks the rollout from this repository, but the setting default is owned by the Python extension and the implementation change must be made in microsoft/vscode-python.

Acceptance criteria:

• Change the default value of python.useEnvironmentsExtension from false to true in the Python extension.
• Verify users with telemetry and experiments disabled use the Python Environments extension when they have not explicitly configured the setting.
• Preserve an explicit "python.useEnvironmentsExtension": false value as an opt-out.
• Verify the Python extension and Python Environments extension agree on which extension owns environment management after the default changes.
• Add or update tests in the Python extension that cover the new default and the explicit opt-out.
• Coordinate the Python extension release containing the change and close this tracking issue once it is available.

Related: #1778, #1892