Switch wslinfo --vm-id to not rely on presence of VM ID environment variable

[benhillis]

This change is a follow up from #13212. This is preferred because it discourages users of WSL from making assumptions about what environment variables may be present, which is fragile because processes can and do modify their environment.

[benhillis]

Still need an updated WSLg to make this work.

[Copilot]

Pull Request Overview

This PR changes wslinfo --vm-id to query the VM ID directly from the init process rather than relying on the WSL2_VM_ID environment variable, making the implementation more robust and discouraging fragile assumptions about environment variables.

• Adds a new message type LxInitMessageQueryVmId for querying VM ID from the init process
• Implements UtilGetVmId() function to communicate with init via socket channel
• Updates test to validate VM ID format and ensure environment variable is not exposed to user commands

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/windows/UnitTests.cpp	Updates test to validate VM ID format and verify environment variable is not propagated to user commands
src/shared/inc/lxinitshared.h	Adds new message type and struct for VM ID queries
src/linux/init/wslinfo.cpp	Changes VM ID retrieval to use new UtilGetVmId() function instead of environment variable
src/linux/init/util.h	Declares new UtilGetVmId() function
src/linux/init/util.cpp	Implements UtilGetVmId() to query VM ID from init process via socket
src/linux/init/main.cpp	Adds WSL2_SYSTEM_DISTRO environment variable for system distros
src/linux/init/init.cpp	Stores VM ID in config and conditionally unsets environment variable for user distros
src/linux/init/config.cpp	Handles VM ID query messages and removes VM ID from environment block
src/linux/init/WslDistributionConfig.h	Adds optional VM ID field to configuration struct