Feat/add vs2026 support

[keelbismark]

Checklist

• npm install && npm run lint && npm test passes
• tests are included
• documentation is changed or added
• commit message follows commit guidelines

Description of change

feat: add support for Visual Studio 2026

This pull request introduces initial support for the upcoming Visual Studio 2026 (internal version 18.0).

The key changes include:

• Version Detection: Added '2026' and version '18.0' to the version maps in SelectVisualStudioVersion and _DetectVisualStudioVersions. This allows GYP to correctly identify VS 2026 installations.
• Version Creation: Included a new VisualStudioVersion definition for '2026' in the _CreateVersion function.
• Toolset Update: Set the default_toolset to v145. This aligns with the toolset version observed in the Visual Studio 2026 Insider Preview builds, resolving potential MSB8020 errors for users on the latest previews.

These changes enable developers using early versions of Visual Studio 2026 to generate and build projects with GYP seamlessly.

[cclauss]

@StefanStojanovic, your review please. There are an increasing number of Visual Studio not found issues.

[StefanStojanovic]

@cclauss I've already approved these changes in gyp-next. It was my understanding that we should land them there and pull them to node-gyp as gyp-next update afterwards. Is this the correct flow?

[lukekarrys]

@StefanStojanovic @cclauss Yeah I think that's what we agreed upon previously. Once landed and released in gyp-next there's a workflow that will automatically update them in this repo.

While on the topic: what do either of you think about a PR check that would detect changes to the gyp/ directory and fail with a message to make the changes to gyp-next instead?

[lukekarrys]

Closing this in favor of #3236

[lukekarrys]

#3236 is now merged and the next release will have support for VS2026