Consume updated Roslyn API

[drewnoakes]

Roslyn created a new API for us to call, as discussed in dotnet/roslyn#78972 (comment)_

We would call it in these two locations:

project-system/src/Microsoft.VisualStudio.ProjectSystem.Managed.VS/ProjectSystem/VS/Properties/StartupObjectsEnumProvider.cs

Line 87 in 05aa251

IEnumerable<INamedTypeSymbol>? entryPoints = entryPointFinderService?.FindEntryPoints(compilation.GlobalNamespace, _searchForEntryPointsInFormsOnly);

project-system/src/Microsoft.VisualStudio.ProjectSystem.Managed.VS/ProjectSystem/VS/Properties/VisualBasic/SplashScreenEnumProvider.cs

Line 86 in 05aa251

IEnumerable<INamedTypeSymbol>? entryPoints = entryPointFinderService?.FindEntryPoints(compilation.GlobalNamespace, _searchForEntryPointsInFormsOnly);