[BUG]`Microsoft.CognitiveServices/accounts/projects` cannot update description and displayName to empty

### API Spec link

https://github.com/Azure/azure-rest-api-specs/blob/d752b87f59f917963d183b9de20677aadf9a965f/specification/cognitiveservices/resource-manager/Microsoft.CognitiveServices/stable/2025-06-01/cognitiveservices.json#L3712

### API Spec version

2025-06-01

### Describe the bug

The PUT or PATCH method cannot update the existing non-empty `description` and `display_name` to empty.

### Expected behavior

The PUT or PATCH method shoube be able to update the existing non-empty `description` and `display_name` to empty.

### Actual behavior

The PUT or PATCH method cannot update the existing non-empty `description` and `display_name` to empty. I have attempted both PUT and PATCH methods, using null, an empty string, or omitting these fields, but none have been successful.

### Reproduction Steps

PUT https://management.azure.com/subscriptions//resourceGroups/acctestRG-cognitive-251020064914004828/providers/Microsoft.CognitiveServices/accounts/acctest-cog-251020064914004828/projects/acctest-project-251020064914004828?api-version=2025-06-01 HTTP/2.0
content-type: application/json; charset=utf-8
user-agent: HashiCorp/go-azure-sdk (Go-http-Client/1.1 cognitiveservicesprojects/2025-06-01) HashiCorp Terraform/1.13.3 (+https://www.terraform.io) terraform-provider-azurerm/acc pid-222c6c49-1b0a-5959-a213-6608f9eb8820
x-ms-correlation-request-id: 226e2d15-6f56-b86f-5ad3-cea85c6470a0
content-length: 744
accept-encoding: gzip

```json
{
"etag": "\"a2019f69-0000-0200-0000-68f5dbfd0000\"",
"id": "/subscriptions//resourceGroups/acctestRG-cognitive-251020064914004828/providers/Microsoft.CognitiveServices/accounts/acctest-cog-251020064914004828/projects/acctest-project-251020064914004828",
"identity": {
"type": "SystemAssigned",
"userAssignedIdentities": null
},
"location": "eastus2",
"name": "acctest-cog-251020064914004828/acctest-project-251020064914004828",
"properties": {
"endpoints": {
"AI Foundry API": "https://acctestaiservices-251020064914004828.services.ai.azure.com/api/projects/acctest-project-251020064914004828"
},
"isDefault": true,
"provisioningState": "Succeeded"
},
"systemData": null,
"tags": {

},
"type": "Microsoft.CognitiveServices/accounts/projects"
}
```

HTTP/2.0 200
cache-control: no-cache
pragma: no-cache
content-length: 1229
content-type: application/json; charset=utf-8
expires: -1
etag: "a201416c-0000-0200-0000-68f5dc2e0000"
x-content-type-options: nosniff
x-ms-request-id: 7cf42a42-2294-4e93-91b3-5b7a6afa2f75
x-envoy-upstream-service-time: 5447
x-ms-operation-identifier: appId=fbc3e9cf-9e1b-41a4-b081-98024ff6cc20,tenantId=7b31ddc4-9101-4ef0-a387-79ce181cacdb,objectId=8c349b5f-169d-4b61-baca-f41ee1db4e46/eastus2/f90bf640-752e-4aba-be44-8f3fbc73ef57
x-ms-ratelimit-remaining-subscription-writes: 199
x-ms-ratelimit-remaining-subscription-global-writes: 2999
x-ms-correlation-request-id: 226e2d15-6f56-b86f-5ad3-cea85c6470a0
x-ms-routing-request-id: EASTUS2:20251020T065230Z:caa6344e-135a-474f-adfd-d0de99df2b5f
strict-transport-security: max-age=31536000; includeSubDomains
x-cache: CONFIG_NOCACHE
x-msedge-ref: Ref A: 3D45E850BC084DC7BD933308A1F49426 Ref B: SYD03EDGE0819 Ref C: 2025-10-20T06:52:24Z
date: Mon, 20 Oct 2025 06:52:30 GMT

```json
{
"id": "/subscriptions//resourceGroups/acctestRG-cognitive-251020064914004828/providers/Microsoft.CognitiveServices/accounts/acctest-cog-251020064914004828/projects/acctest-project-251020064914004828",
"name": "acctest-cog-251020064914004828/acctest-project-251020064914004828",
"type": "Microsoft.CognitiveServices/accounts/projects",
"etag": "\"a201416c-0000-0200-0000-68f5dc2e0000\"",
"location": "eastus2",
"kind": "AIServices",
"tags": {

},
"properties": {
"endpoints": {
"AI Foundry API": "https://acctestaiservices-251020064914004828.services.ai.azure.com/api/projects/acctest-project-251020064914004828"
},
"description": "Updated project description",
"displayName": "Updated Project Display",
"isDefault": true,
"internalId": "9cfe921e26dd4485a926929c8f7ade54",
"provisioningState": "Succeeded"
},
"identity": {
"principalId": "8e66293f-a808-4283-a37f-c5a7f927cfaa",
"tenantId": "7b31ddc4-9101-4ef0-a387-79ce181cacdb",
"type": "SystemAssigned"
},
"systemData": {
"createdBy": "fbc3e9cf-9e1b-41a4-b081-98024ff6cc20",
"createdByType": "Application",
"createdAt": "2025-10-20T06:49:56.3915274Z",
"lastModifiedBy": "fbc3e9cf-9e1b-41a4-b081-98024ff6cc20",
"lastModifiedByType": "Application",
"lastModifiedAt": "2025-10-20T06:49:56.3915274Z"
}
}
```

### Environment

Terraform

Start with the 2025-06-01 cognitiveservices.json specification at line 3712, then reproduce the PUT and PATCH requests described in the issue. Check how empty description and displayName values are represented in the project schema and responses. Done means the service behavior and API specification consistently allow both existing fields to be cleared.

Written by the indexing model from the issue text.