Upgrade the targetframe from 4.5 to 4.8.x since v4.5 is out of service

[xuzhg]

trafficstars

Short summary (3-5 sentences) describing the issue.

Assemblies affected

*Which assemblies and versions are known to be affected e.g. OData WebApi lib 6.1.0

Reproduce steps

The simplest set of steps to reproduce the issue. If possible, reference a commit that demonstrates the issue.

Expected result

What would happen if there wasn't a bug.

Actual result

What is actually happening.

Additional detail

Optional, details of the root cause if known. Delete this section if you have no additional details to add.

[ificator]

If this applies to 7.5.x it will block OneDrive from updating due to some dependencies on 4.5. We're hoping to have those gone by H2 2022.

[commonsensesoftware]

While there could be benefits to targeting .NET 4.8 those are not being stated here. As long as ASP.NET Web API still targets .NET 4.5, the target should not be eliminated. If you want to take advantage of newer features, then adding a target for .NET 4.8 can address that. Forcing this on consumers can cause a myriad of problems. Continuing to target .NET 4.5 requires nothing more than adding the NuGet package reference for the Reference Assemblies. You don't need .NET 4.5 installed nor any special flavor of Visual Studio to build it. You never know who, how, or why developers are still using .NET 4.5. Sometimes there are valid reasons. If you're not intending to use newer features, imposing this change on everyone has little benefit. If there is some truly compelling reason for this change it, should be made clear; especially, if you won't multi-target. This change also affects any extension or customization library for OData.