Bug: VertexAIEmbeddingGenerator hardcodes :predict, unusable with gemini-embedding models that only serve :embedContent #14265

#:package Microsoft.SemanticKernel.Connectors.Google@1.75.0-alpha
#:property NoWarn=SKEXP0001;SKEXP0070

using System.Net.Http.Json;
using System.Text.Json;
using Microsoft.Extensions.AI;
using Microsoft.SemanticKernel;
using Microsoft.SemanticKernel.Connectors.Google;

const string ModelId = "gemini-embedding-2";
const int Dimensions = 768;

var token     = Require("GOOGLE_ACCESS_TOKEN");
var projectId = Require("GOOGLE_PROJECT_ID");
var location  = Environment.GetEnvironmentVariable("GOOGLE_LOCATION") is { Length: > 0 } l ? l : "us-central1";

Console.WriteLine($"model={ModelId} project={projectId} location={location} dimensions={Dimensions}");
Console.WriteLine($"SK Connectors.Google = {typeof(VertexAIEmbeddingGenerator).Assembly.GetName().Version}");
Console.WriteLine();

try
{
    IEmbeddingGenerator<string, Embedding<float>> generator = new VertexAIEmbeddingGenerator(
        modelId:    ModelId,
        bearerKey:  token,
        location:   location,
        projectId:  projectId,
        dimensions: Dimensions);

    var embeddings = await generator.GenerateAsync(["test"]);
    Console.WriteLine($"    UNEXPECTED SUCCESS: {embeddings[0].Vector.Length} floats");
}
catch (HttpOperationException ex)
{
    Console.WriteLine($"    FAILED  status={ex.StatusCode}");
    Console.WriteLine($"    message={ex.Message}");
    Console.WriteLine($"    body={Trim(ex.ResponseContent)}");
}
catch (Exception ex)
{
    Console.WriteLine($"    FAILED  {ex.GetType().Name}: {ex.Message}");
}