The `$(Configuration)` variable is not set when loading C# projects

## Issue Description ##

The `$(Configuration)` variable is not set when loading C# projects

When omnisharp loads a project the `$(Configuration)` variable is not set, this can result in errors loading a project, In my case I trying to load a MSBuild task from `$(MSBuildThisFileDirectory)bin\$(Configuration)\netstandard2.0\MyTask.dll`. The project builds fine from the command line and with MSBuild, but with omnisharp it fails to load the task because `$(Configuration)` is expanded to an empty string.

## Environment information ##

**VSCode version**: 1.77.0
**C# Extension**: 1.25.4

Dotnet Information
.NET SDK:
Version: 7.0.202
Commit: 6c74320bc3

Runtime Environment:
OS Name: Windows
OS Version: 10.0.19044
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\7.0.202\

Host:
Version: 7.0.4
Architecture: x64
Commit: 0a396acafe

.NET SDKs installed:
5.0.416 [C:\Program Files\dotnet\sdk]
6.0.302 [C:\Program Files\dotnet\sdk]
7.0.202 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.14 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 3.1.20 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.14 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.20 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.14 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.15 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.4 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
x86 [C:\Program Files (x86)\dotnet]
registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
Not set

global.json file:
Not found

Learn more:
https://aka.ms/dotnet/info

Download .NET:
https://aka.ms/dotnet/download

Visual Studio Code Extensions

|Extension|Author|Version|
|---|---|---|
|better-cpp-syntax|jeff-hykin|1.17.2|
|cmake|twxs|0.0.17|
|cmake-language-support-vscode|josetr|0.0.9|
|cmake-tools|ms-vscode|1.13.45|
|code-spell-checker|streetsidesoftware|2.20.4|
|cpptools|ms-vscode|1.14.5|
|cpptools-extension-pack|ms-vscode|1.3.0|
|cpptools-themes|ms-vscode|2.0.0|
|csharp|ms-dotnettools|1.25.4|
|dart-code|Dart-Code|3.60.1|
|doxdocgen|cschlosser|1.4.0|
|EditorConfig|EditorConfig|0.16.4|
|flutter|Dart-Code|3.60.0|
|intellicode-api-usage-examples|VisualStudioExptTeam|0.2.7|
|isort|ms-python|2022.8.0|
|java|redhat|1.16.0|
|jupyter|ms-toolsai|2023.3.1000892223|
|powershell|ms-vscode|2023.3.3|
|python|ms-python|2023.6.0|
|remote-containers|ms-vscode-remote|0.288.0|
|remote-explorer|ms-vscode|0.2.0|
|remote-ssh|ms-vscode-remote|0.98.0|
|remote-wsl|ms-vscode-remote|0.77.0|
|rust-analyzer|rust-lang|0.3.1459|
|vscode-docker|ms-azuretools|1.24.0|
|vscode-dotnet-runtime|ms-dotnettools|1.6.0|
|vscode-java-debug|vscjava|0.49.1|
|vscode-java-dependency|vscjava|0.21.2|
|vscode-java-pack|vscjava|0.25.10|
|vscode-java-test|vscjava|0.38.2|
|vscode-jupyter-cell-tags|ms-toolsai|0.1.8|
|vscode-jupyter-slideshow|ms-toolsai|0.1.5|
|vscode-maven|vscjava|0.41.0|
|vscode-pylance|ms-python|2023.3.40|
|vscodeintellicode|VisualStudioExptTeam|1.2.30|;