Vaihi add langmodel types. (#8927)

* Adding LanguageModel types. These are based off https://github.com/webmachinelearning/prompt-api?tab=readme-ov-file#full-api-surface-in-web-idl

* Adding LanguageModel types.

* Remove bunch of exports

* yarn formatted

* after lint

Author: gsiddh

packages/vertexai/src/types/language-model.ts

@@ -0,0 +1,83 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+export interface LanguageModel extends EventTarget {
+  create(options?: LanguageModelCreateOptions): Promise<LanguageModel>;
+  availability(options?: LanguageModelCreateCoreOptions): Promise<Availability>;
+  prompt(
+    input: LanguageModelPrompt,
+    options?: LanguageModelPromptOptions
+  ): Promise<string>;
+  promptStreaming(
+    input: LanguageModelPrompt,
+    options?: LanguageModelPromptOptions
+  ): ReadableStream;
+  measureInputUsage(
+    input: LanguageModelPrompt,
+    options?: LanguageModelPromptOptions
+  ): Promise<number>;
+  destroy(): undefined;
+}
+enum Availability {
+  'unavailable',
+  'downloadable',
+  'downloading',
+  'available'
+}
+interface LanguageModelCreateCoreOptions {
+  topK?: number;
+  temperature?: number;
+  expectedInputs?: LanguageModelExpectedInput[];
+}
+interface LanguageModelCreateOptions extends LanguageModelCreateCoreOptions {
+  signal?: AbortSignal;
+  systemPrompt?: string;
+  initialPrompts?: LanguageModelInitialPrompts;
+}
+interface LanguageModelPromptOptions {
+  signal?: AbortSignal;
+}
+interface LanguageModelExpectedInput {
+  type: LanguageModelMessageType;
+  languages?: string[];
+}
+type LanguageModelPrompt =
+  | LanguageModelMessage[]
+  | LanguageModelMessageShorthand[]
+  | string;
+type LanguageModelInitialPrompts =
+  | LanguageModelMessage[]
+  | LanguageModelMessageShorthand[];
+interface LanguageModelMessage {
+  role: LanguageModelMessageRole;
+  content: LanguageModelMessageContent[];
+}
+interface LanguageModelMessageShorthand {
+  role: LanguageModelMessageRole;
+  content: string;
+}
+interface LanguageModelMessageContent {
+  type: LanguageModelMessageType;
+  content: LanguageModelMessageContentValue;
+}
+type LanguageModelMessageRole = 'system' | 'user' | 'assistant';
+type LanguageModelMessageType = 'text' | 'image' | 'audio';
+type LanguageModelMessageContentValue =
+  | ImageBitmapSource
+  | AudioBuffer
+  | BufferSource
+  | string;