Add support for .NET 4.8 and remove support for .NET 4.7.2

## Detailed Description

We need to change to use the long term supported version of the .NET Framework.

## Context

.NET 4.8 is the most recent version of .NET Framework, and the one that has long term support, so we should switch to requiring this.

## Possible Implementation

Change TargetFrameworks and remove usage of .NET 4.7.2.

## Your Environment

N/A