Visual Studio 2026 Extension

**Is your feature request related to a problem? Please describe.**
I am evaluating [Visual Studio 2026 Insiders](https://devblogs.microsoft.com/visualstudio/visual-studio-2026-insiders-is-here/) and would like to use the [ms-azuretools.visualstudiobicep](https://marketplace.visualstudio.com/items?itemName=ms-azuretools.visualstudiobicep) marketplace extension.

VS 2022 extensions are supposedly compatible, so hopefully there is no additional work required other than relaxing the exclusive version range constraints[¹](https://learn.microsoft.com/en-us/nuget/concepts/package-versioning?tabs=semver20sort#version-ranges).

**Describe the solution you'd like**
Update the extension.vsixmanifest to properly support 18.0

https://github.com/Azure/bicep/blob/387808a9056ad99eeef09fa8f0e7f8afe90742f2/src/vs-bicep/Bicep.VSLanguageServerClient.Vsix/source.extension.vsixmanifest#L11
https://github.com/Azure/bicep/blob/387808a9056ad99eeef09fa8f0e7f8afe90742f2/src/vs-bicep/Bicep.VSLanguageServerClient.Vsix/source.extension.vsixmanifest#L24

Open src/vs-bicep/Bicep.VSLanguageServerClient.Vsix/source.extension.vsixmanifest and inspect the version constraints at the referenced lines. Update the manifest to support Visual Studio 18.0, then verify that the extension can be installed or recognized by Visual Studio 2026 Insiders.

Written by the indexing model from the issue text.