Update solutions to support the Visual Studio 2026 IDE project/solution format of ver. 18.x+

[raman-m]

Alongside the release of the .NET 10 SDK (aka net10.0 TFM for .NET 10 LTS), the long-awaited major update of Visual Studio 2026 launched on November 24, 2025.

• The current version is the December Update 18.1.0, effective December 9, 2025.

Goals

1. With the major .NET 10 LTS release and the launch of Visual Studio 2026, Ocelot solutions need to be updated to align with the .NET 10 environment that the community will use when working with Ocelot's .NET 10 version.
2. Visual Studio 2026 also brings a new .slnx XML solution format to replace the older .sln, keeping project files the same but making solution management easier, cleaner, and less prone to errors. More details → New, Simpler Solution File Format