[tcgc] export SdkEmitterOptionsSchema (#2393)

Export `SdkEmitterOptionsSchema` for downstream emitter to add same
options.

Author: tadelesh

.chronus/changes/export_schema-2025-2-17-11-42-28.md

@@ -0,0 +1,7 @@
+---
+changeKind: feature
+packages:
+  - "@azure-tools/typespec-client-generator-core"
+---
+
+Export `SdkEmitterOptionsSchema` for downstream emitter to add same options.

packages/typespec-client-generator-core/src/lib.ts

@@ -1,9 +1,9 @@
 import { createTypeSpecLibrary, JSONSchemaType, paramMessage } from "@typespec/compiler";
 import { SdkEmitterOptions } from "./interfaces.js";
 
-const EmitterOptionsSchema: JSONSchemaType<SdkEmitterOptions> = {
+export const SdkEmitterOptionsSchema: JSONSchemaType<SdkEmitterOptions> = {
   type: "object",
-  additionalProperties: true,
+  additionalProperties: false,
   properties: {
     "emitter-name": {
       type: "string",
@@ -315,7 +315,7 @@ export const $lib = createTypeSpecLibrary({
     },
   },
   emitter: {
-    options: EmitterOptionsSchema as JSONSchemaType<SdkEmitterOptions>,
+    options: SdkEmitterOptionsSchema,
   },
 });