[Bug] Metadata extraction fails when C# projects pull in a newer compiler than DocFX ships with

**Describe the bug**
When a project explicitly references the `Microsoft.Net.Compilers.Toolset` package to pull in a specific version of Roslyn, if that version is newer than the version DocFX ships with (and there are source generators that depend on that version), metadata extraction fails because the source generator assemblies can't be loaded.

**To Reproduce**
Steps to reproduce the behavior:
1. Create a project referencing the latest version of `Microsoft.Net.Compilers.Toolset`:
```xml

```
as well as a source generator that references that same version:
```xml

```
2. Build the project normally, it will succeed.
3. Use DocFX to extract metadata from the non-SG project, it will fail (if there is code that references generated content).

**Expected behavior**
No failures when building metadata for a project which builds successfully.

**Context (please complete the following information):**
- OS: All
- Docfx version: 2.77.0
- .NET version: .NET SDK 8.0.401

This was found from the MonoMod project, when I upgraded Roslyn most recently: https://github.com/MonoMod/MonoMod/actions/runs/10725450864/job/29743290858

I have a workaround [here](https://github.com/MonoMod/MonoMod/pull/191), which forcibly downgrades Roslyn to the version shipped with DocFX when performing the docs build.

If testing on [MonoMod](https://github.com/MonoMod/MonoMod), the behavior can be seen with:
```
$ dotnet tool restore
$ dotnet build -c Release -p:RunAnalyzers=false
$ dotnet docfx docfx/docfx.json
```

dotnet --info

```
.NET SDK:
Version: 8.0.401
Commit: 811edcc344
Workload version: 8.0.400-manifests.57f7c351
MSBuild version: 17.11.4+37eb419ad

Runtime Environment:
OS Name: Windows
OS Version: 10.0.19045
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\8.0.401\

.NET workloads installed:
Configured to use loose manifests when installing new manifests.
[android]
Installation Source: SDK 8.0.400, VS 17.12.35209.166
Manifest Version: 34.0.113/8.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.android\34.0.113\WorkloadManifest.json
Install Type: FileBased

[aspire]
Installation Source: SDK 8.0.400, VS 17.11.35222.181
Manifest Version: 8.2.0/8.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.aspire\8.2.0\WorkloadManifest.json
Install Type: FileBased

[ios]
Installation Source: SDK 8.0.400, VS 17.12.35209.166
Manifest Version: 17.5.8020/8.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.ios\17.5.8020\WorkloadManifest.json
Install Type: FileBased

[maccatalyst]
Installation Source: SDK 8.0.400, VS 17.12.35209.166
Manifest Version: 17.5.8020/8.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.maccatalyst\17.5.8020\WorkloadManifest.json
Install Type: FileBased

[maui-windows]
Installation Source: SDK 8.0.400, VS 17.12.35209.166
Manifest Version: 8.0.72/8.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.maui\8.0.72\WorkloadManifest.json
Install Type: FileBased

Host:
Version: 9.0.0-preview.7.24405.7
Architecture: x64
Commit: static

.NET SDKs installed:
2.1.818 [C:\Program Files\dotnet\sdk]
2.2.402 [C:\Program Files\dotnet\sdk]
3.0.103 [C:\Program Files\dotnet\sdk]
3.1.426 [C:\Program Files\dotnet\sdk]
5.0.408 [C:\Program Files\dotnet\sdk]
6.0.401 [C:\Program Files\dotnet\sdk]
6.0.402 [C:\Program Files\dotnet\sdk]
6.0.425 [C:\Program Files\dotnet\sdk]
7.0.410 [C:\Program Files\dotnet\sdk]
8.0.304 [C:\Program Files\dotnet\sdk]
8.0.400 [C:\Program Files\dotnet\sdk]
8.0.401 [C:\Program Files\dotnet\sdk]
9.0.100-preview.7.24407.12 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.All 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.0.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.29 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
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 6.0.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.10 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.32 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.0-preview.7.24406.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.0.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.29 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.30 [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 6.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.10 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.32 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.0-preview.7.24405.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.0.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.29 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.30 [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 6.0.9 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.10 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.32 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.7 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 9.0.0-preview.7.24405.2 [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:
Y:\src\MonoMod\global.json

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

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