feat(vertex-ai): Refactor Gemini for new tool calling API

- Migrate from function calling to tool calling API
- Add support for Gemini 2.0 models (flash, flash-lite)
- Implement JSON schema to OpenAPI schema conversion
- Add builder pattern for improved configuration
- Deprecate legacy function calling constructors and methods
- Update default model to GEMINI_2_0_FLASH
- Add comprehensive test coverage for tool calling
- Upgrade victools dependency to 4.37.0
- Update the Vertex Tool calling docs

Part of the #2207 epic

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>

spring-ai-core/src/main/java/org/springframework/ai/util/json/schema/JsonSchemaGenerator.java

@@ -244,7 +244,7 @@ public final class JsonSchemaGenerator {
 	}
 
 	// Based on the method in ModelOptionsUtils.
-	private static void convertTypeValuesToUpperCase(ObjectNode node) {
+	public static void convertTypeValuesToUpperCase(ObjectNode node) {
 		if (node.isObject()) {
 			node.fields().forEachRemaining(entry -> {
 				JsonNode value = entry.getValue();