Fix legacy caching module distribution for CI

The legacy caching bundle at sources/legacy-caching/dist/ was
gitignored by sources/.gitignore, so CI never included it. Fix by:
- Copying the bundle into sources/dist/legacy-caching/ during build
- Updating the loader path to resolve from dist/legacy-caching/
- Adding legacy module build steps to build-dist action and
  ci-update-dist workflow

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sources/legacy-caching/src/gradle-utils.ts

@@ -90,16 +90,6 @@ export function findGradleExecutableForCleanup(buildResults: BuildResults): stri
         }
     }
 
-    // Try the Gradle installation directory as a fallback
-    for (const result of buildResults.results) {
-        if (versionIsAtLeast(result.gradleVersion, '8.11')) {
-            const executable = path.resolve(result.gradleHomeDir, 'bin', IS_WINDOWS ? 'gradle.bat' : 'gradle')
-            if (fs.existsSync(executable)) {
-                return executable
-            }
-        }
-    }
-
     core.info('Could not locate a Gradle >= 8.11 executable for cache cleanup.')
     return null
 }

sources/src/cache-service-loader.ts

@@ -75,7 +75,7 @@ export async function loadVendoredCacheService(): Promise<CacheService> {
 }
 
 export async function loadLegacyCacheService(): Promise<CacheService> {
-    const legacyLibraryPath = findLibraryPath('sources/legacy-caching/dist/index.js')
+    const legacyLibraryPath = findLibraryPath('dist/legacy-caching/index.js')
     const moduleUrl = pathToFileURL(legacyLibraryPath).href
     return (await import(moduleUrl)) as CacheService
 }