Add PatternPropertiesExtension to public API

Update PublicAPI.Shipped.txt to include Microsoft.OpenApi.OpenApiConstants.PatternPropertiesExtension mapping to "x-jsonSchema-patternProperties" (string!). This exposes the new constant in the shipped public API for the patternProperties extension used by OpenAPI JSON Schema serialization.

Author: mdaneri

src/Microsoft.OpenApi/PublicAPI.Shipped.txt

@@ -2033,3 +2033,4 @@ Microsoft.OpenApi.OpenApiSchemaReference.UnevaluatedPropertiesSchema.get -> Micr
 Microsoft.OpenApi.OpenApiSecurityScheme.OAuth2MetadataUrl.get -> System.Uri?
 Microsoft.OpenApi.OpenApiSecurityScheme.OAuth2MetadataUrl.set -> void
 Microsoft.OpenApi.OpenApiSecuritySchemeReference.OAuth2MetadataUrl.get -> System.Uri?
+const Microsoft.OpenApi.OpenApiConstants.PatternPropertiesExtension = "x-jsonSchema-patternProperties" -> string!