Export and use utility functions from lib/utils

Export `createStateSymbol` from `lib/utils`, and export all of utils in `@typespec/compiler` so they can be used by other packages.

Additionally, replace duplicate definitions of `utils` functions in `@typespec/compiler` with imports from `utils`.

packages/compiler/src/index.ts

@@ -1,6 +1,7 @@
 export { resolveCompilerOptions, ResolveCompilerOptionsOptions } from "./config/index.js";
 export * from "./core/index.js";
 export * from "./lib/decorators.js";
+export * from "./lib/utils.js";
 export * from "./server/index.js";
 export type { PackageJson } from "./types/package-json.js";
 import * as formatter from "./formatter/index.js";

packages/compiler/src/lib/decorators.ts

@@ -99,7 +99,12 @@ import {
   Value,
 } from "../core/types.js";
 import { setKey } from "./key.js";
-import { useStateMap, useStateSet } from "./utils.js";
+import {
+  createStateSymbol,
+  filterModelPropertiesInPlace,
+  useStateMap,
+  useStateSet,
+} from "./utils.js";
 
 export { $encodedName, resolveEncodedName } from "./encoded-names.js";
 export { serializeValueAsJson } from "./examples.js";
@@ -121,10 +126,6 @@ function replaceTemplatedStringFromProperties(formatString: string, sourceObject
   });
 }
 
-export function createStateSymbol(name: string) {
-  return Symbol.for(`TypeSpec.${name}`);
-}
-
 const [getSummary, setSummary] = useStateMap<Type, string>("summary");
 /**
  * @summary attaches a documentation string. It is typically used to give a short, single-line
@@ -810,17 +811,6 @@ function validateEncodeData(context: DecoratorContext, target: Type, encodeData:
 
 export { getEncode };
 
-export function filterModelPropertiesInPlace(
-  model: Model,
-  filter: (prop: ModelProperty) => boolean,
-) {
-  for (const [key, prop] of model.properties) {
-    if (!filter(prop)) {
-      model.properties.delete(key);
-    }
-  }
-}
-
 // -- @withOptionalProperties decorator ---------------------
 
 export const $withOptionalProperties: WithOptionalPropertiesDecorator = (

packages/compiler/src/lib/utils.ts

@@ -1,7 +1,7 @@
 import type { Model, ModelProperty, Type } from "../core/types.js";
 import { unsafe_useStateMap, unsafe_useStateSet } from "../experimental/state-accessor.js";
 
-function createStateSymbol(name: string) {
+export function createStateSymbol(name: string) {
   return Symbol.for(`TypeSpec.${name}`);
 }