Normalization of GitVersionTargetFramework and fallback scenario

[samtrion]

This is about making sure that compatible target frameworks are treated equally. The previous solution tried to use the TargetFramework, which led to an error when we used net8.0-windows.

Description

The solution here normalizes net8.0-windows and all other platform-specific TargetFrameworks to
net8.0. It also accounts for net9.0 or higher. If the TargetFramework isn't compatible with net8.0, it checks for compatibility with net6.0. If that doesn't work, it falls back to net8.0.

Related Issue

#4192

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Checklist:

• My code follows the code style of this project.

In this case not necessary, i think.

• 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.