Refactoring DiagnosticDescriptors.cs files

[benhopkinstech]

I noticed that there are several DiagnosticDescriptor.cs files across the solution, and I believe there are a couple improvements we can make.

For example, we have many repeated strings across descriptors, so we could introduce constants to maintain consistency.

Additionally, where we're using LocalizableResourceString, we could create a helper method to make the code more concise.

I also considered creating a complete helper method to generate the descriptors, but I believe the current structure is more readable and easier to understand.