Fix E_ACCESSDENIED during download if temp is hidden

[chemwolf6922]

Summary of the Pull Request

The winrt::Windows::Storage::StorageFolder::GetFolderFromPathAsync function does not accept folders with hidden or system attributes. To solve that, this PR creates a sub folder under temp without those attributes and use that for the winrt functions.

PR Checklist

• Closes: cannot use wsl --update to update WSL, nor use wsl --install to install a Linux distribution #40662
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

Add test UnitTests::UnitTests::ModernDistroInstallWithHiddenTempFolder

[Copilot]

Pull request overview

This PR addresses E_ACCESSDENIED failures during wsl --update / wsl --install downloads when the user’s temp directory has the Hidden/System attributes set, by switching WinRT file operations to a newly-created temp subfolder with those attributes cleared.

Changes:

• Refactors the existing modern distro install unit test logic into a helper so it can be reused by multiple test cases.
• Adds a new unit test that exercises modern distro installation when the temp folder is hidden.
• Updates the WinRT download path selection to use a wsl-downloads subfolder under %TEMP%, explicitly clearing Hidden/System attributes before calling StorageFolder::GetFolderFromPathAsync.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
test/windows/UnitTests.cpp	Refactors the ModernDistroInstall test and adds a regression test for hidden temp folders.
src/windows/common/wslutil.cpp	Routes WinRT-based downloads through a temp subfolder with Hidden/System attributes cleared.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

[benhillis]

Looks good maybe just drop the set when it is not needed.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.