Drop support of PowerShell 3, 4, 6.2, and unsupported 7

[nohwnd]

PR Summary

Remove testing on unsupported versions of Windows PowerShell 3, 4 and PowerShell 6.2, so we only support 5.1, 7.2 and newer based on their lifetimes.

Update TFMs to reflect the supported .NET and .NET Framework versions. Use non-vulnerable packages.

Use embedded PDBs.

PR Checklist

• PR has meaningful title
• Summary describes changes
• PR is ready to be merged
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• Tests are added/update (if required)
• Documentation is updated/added (if required) <- Not yet, that will be a whole other PR to docs after this is fully released.

[fflaten]

Should we let this stabilize for a patch or minor release before starting cleanup of PS 3/4 logic and syntax (like New-Object -> ::new()) ?

[nohwnd]

This was reverted in 5.6.0, but was reapplied on main for 6.0.0 and newer.