Support semantic token for `| null`

[MangelMaxime]

Version

Ionide 7.26.4

Dotnet Info

.NET SDK:
Version: 9.0.302
Commit: bb2550b9af
Workload version: 9.0.300-manifests.fadeff71
MSBuild version: 17.14.13+65391c53b

Runtime Environment:
OS Name: arch
OS Version:
OS Platform: Linux
RID: linux-x64
Base Path: /home/mmangel/.dotnet/sdk/9.0.302/

.NET workloads installed:
There are no installed workloads to display.
Configured to use loose manifests when installing new manifests.

Host:
Version: 9.0.7
Architecture: x64
Commit: 3c298d9f00

.NET SDKs installed:
6.0.428 [/home/mmangel/.dotnet/sdk]
7.0.410 [/home/mmangel/.dotnet/sdk]
8.0.408 [/home/mmangel/.dotnet/sdk]
9.0.203 [/home/mmangel/.dotnet/sdk]
9.0.302 [/home/mmangel/.dotnet/sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 6.0.36 [/home/mmangel/.dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.20 [/home/mmangel/.dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.15 [/home/mmangel/.dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.4 [/home/mmangel/.dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.7 [/home/mmangel/.dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 6.0.36 [/home/mmangel/.dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.20 [/home/mmangel/.dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.15 [/home/mmangel/.dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.4 [/home/mmangel/.dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.7 [/home/mmangel/.dotnet/shared/Microsoft.NETCore.App]

Other architectures found:
None

Environment variables:
DOTNET_ROOT [/home/mmangel/.dotnet]

global.json file:
Not found

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Steps to reproduce

1. Write the following code

let toUpper (txt : string | null) = ()

2. Move cursor to null
3. In Ionide, execute the command Inspect editor tokens [...]

See that for string we get semantic token type

but not for null

Details

null should have a semantic token type information like string

Or perhaps we should cover sting | null as a single semantic token type

Logs

No response

Checklist

• I have looked through existing issues to make sure that this bug has not been reported before
• I have provided a descriptive title for this issue
• I have made sure that that this bug is reproducible on the latest version of the package
• I have provided all the information needed to reproduce this bug as efficiently as possible
• I or my company would be willing to contribute this fix