Do not verify existence of LocalApplicationData directory in dotnetup

[lbussell]

Fixes:

• dotnetup can not determine the local application data directory (WSL, Ubuntu 26.04) #54509
• BCL GetFolderPath APIs may return empty paths, which dotnetup interprets as an error #54493

Supersedes #54510

[baronfel]

LGTM!

Style nit (for dotnetup, not your change specifically): I don't like how default-path computation is so spread out - feels like we had to whack-a-mole a bit to find all the places that could hit this issue. Could/should these be centralized/co-located?

[Copilot]

Pull request overview

Fixes dotnetup crashing on minimal Linux environments where ~/.local/share doesn't exist by using Environment.SpecialFolderOption.DoNotVerify when resolving LocalApplicationData, so the path is computed rather than returned as empty. Directory creation is already deferred to write-time helpers.

Changes:

• DotnetupPaths.GetBaseDirectory() now passes DoNotVerify.
• DotnetupTelemetry.s_defaultStorageDirectory now passes DoNotVerify.
• DownloadCache default cache path now passes DoNotVerify, with a comment explaining why it can't reuse DotnetupPaths.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/Installer/dotnetup.Library/DotnetupPaths.cs	Primary fix: resolve LocalApplicationData without verifying existence.
src/Installer/dotnetup.Library/Telemetry/DotnetupTelemetry.cs	Same fix applied to the telemetry default storage directory.
src/Installer/Microsoft.Dotnet.Installation/Internal/DownloadCache.cs	Same fix applied to default download cache path; added comment explaining layering.

[lbussell]

LGTM!

Style nit (for dotnetup, not your change specifically): I don't like how default-path computation is so spread out - feels like we had to whack-a-mole a bit to find all the places that could hit this issue. Could/should these be centralized/co-located?

I think you could easily have everything centralized if you:

• Move DotnetupTelemetry's default directory into DotnetupPaths.
• Remove the default cache directory from Microsoft.DotNet.Installation. Having it default to a dotnetup directory seems kind of odd, if it's intended to be general-use (I'm not sure what the intention is).