[dotnet] Fix building errors of the solution in VS via isolating output path per project

[nvborisenko]

Description

This PR fixes errors like

Motivation and Context

WebDriver.NET solution consists of many projects, and each of them has one shared folder to built into it (/build/dotnet/cli). When we build solution, there is a chance to get inconsistent build process like:

• files are always overridden
• especially when building projects concurrently

Microsoft paid an attention on this situation

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[diemol]

Thank you, @nvborisenko!