Add support for MSBuildTask for VS2026

[Kielek]

Fixes #1566

Add support for MSBuildTask for VS2026.

Now, there is no possibility to use 2026 without manually setting paths.

While reviewing, consider checking commit by commit. It brings explanations for the particular steps.

Needed for https://github.com/open-telemetry/opentelemetry-dotnet-instrumentation

I confirm that the pull-request:

• Follows the contribution guidelines
• Is based on my own work
• Is in compliance with my employer

[Kielek]

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