Propagate x-ms-dynamic-schema through $ref resolution for body parameters

[EricBuist]

When a body schema uses $ref (e.g., Excel Online's Item definition), x-ms-dynamic-schema lives on the referenced definition, not on its individual properties. The decomposition into property parameters was losing this extension, causing ContainsDynamicSchemaOrProperty to be false and preventing dynamic schema tool generation.

In ConnectorFunction.cs:1646, when the body of an OpenAPI operation has properties (e.g. bodySchema.Properties.Any()), PowerFx decomposes the body into individual property parameters. Each synthesized OpenApiParameter gets Extensions = bodyPropertySchema.Extensions — the extensions from the individual property schema, not from the parent body schema.

For Excel Online, the body parameter is "schema": { "$ref": "#/definitions/Item" }. The resolved Item definition has x-ms-dynamic-schema on itself (the parent), but its child property dynamicProperties does not. So the extension is lost during decomposition.

For SharePoint, the inline body schema has x-ms-dynamic-schema directly, which takes a different code path (schema-less body) where the extension is preserved.

Fix

File: src/libraries/Microsoft.PowerFx.Connectors/ConnectorFunction.cs

Added propagation of x-ms-dynamic-schema and x-ms-dynamic-properties from the parent bodySchema to the synthesized property parameter when the property doesn't already have its own. The extensions dictionary is cloned to avoid mutating the original schema.

Test

File: src/tests/Microsoft.PowerFx.Connectors.Tests.Shared/PowerPlatformConnectorTests.cs

Added ExcelOnlineAddRowV2_ItemParamHasDynamicSchema — a [Theory] with both UseItemDynamicPropertiesSpecialHandling true/false, verifying that SupportsDynamicSchemaOrProperty is true on the item parameter for both AddRowV2 and PatchItem operations.

Fixes AB#37071606

[MikeStall]

Ideally, we fix the swagger.
but a generic fix like this to the library is ok, provided it doesn't break anything else.

We just want to avoid per-connector specific code in the library. (which you avoid here)

[EricBuist]

I agree with that. Even Copilot Studio Engine should be free of connector-specific kludges. I took a look at the Excel Online (business) Swagger and without the PowerFx fix, they would need to move the x-ms-dynamic-schema extension from a commonly used reference to duplicate it in each parameter that needs the schema. Tell me if I'm wrong but seems better to fix it in PowerFx so it is possible reuse the x-ms-dynamic-schema declaration across multiple parameter instances in different operations.