Move MediaUploadHashTests into the cross-platform Swift package

Relocate the String.hash guard test from KeystoneTests to WordPressSharedTests
so it runs under `swift test` at the repo root. #25811 moved the other Gutenberg
tests into GutenbergProcessorsTests but left this one behind — it asserts a
Swift String hash value and has no processor dependency. Drops the vestigial
`@testable import WordPress`.

Author: jkmassel

…res/Gutenberg/MediaUploadHashTests.swift …ssSharedTests/MediaUploadHashTests.swiftTests/KeystoneTests/Tests/Features/Gutenberg/MediaUploadHashTests.swift renamed to Modules/Tests/WordPressSharedTests/MediaUploadHashTests.swift Tests/KeystoneTests/Tests/Features/Gutenberg/MediaUploadHashTests.swift renamed to Modules/Tests/WordPressSharedTests/MediaUploadHashTests.swift

@@ -1,8 +1,6 @@
 import Foundation
 import XCTest
 
-@testable import WordPress
-
 class MediaUploadHashTests: XCTestCase {
 
     override func setUp() {