Move eligible KeystoneTests into the cross-platform Swift package tests

[jkmassel]

Moves 11 test suites — and the sources they exercise — out of the Xcode-only KeystoneTests bundle into WordPressShared, so they run under swift test at the repo root. That's the macOS cross-platform gate added in #25344: it runs on a bare checkout with no Xcode project, no simulator, and no app build, in about 20 seconds. These suites previously only ran inside the full iOS unit-test build.

Summary

• Relocate 12 test files from Tests/KeystoneTests to Modules/Tests/WordPressSharedTests.
• Extract 10 source files from the app target into Modules/Sources/WordPressShared so those tests have a macOS-buildable subject to import.
• Delete 2 stale Keystone duplicates (DictionaryHelpersTests, URLIncrementalFilenameTests) whose WordPressShared copies already ran.
• Adds 41 XCTest cases to the root swift test run; the iOS suite keeps every one of these tests via the existing WordPressSharedTests target in WordPressUnitTests.xctestplan.

What moved

All into WordPressShared, with the test alongside in WordPressSharedTests: Queue, Array extensions, Math extensions, NotificationCenter.observeOnce, LoggingURLRedactor, IncrementalDelay (split out of Delay.swift, leaving the DispatchDelayedAction/DelayStateWrapper GCD helpers in the app), QRLoginURLParser/QRLoginToken, ReaderCSS, SiteCreationHeaderData, DashboardDynamicCardAnalyticsEvent.

The two commits map to these groups: the utility batch, and the Array/Math/NotificationCenter/IncrementalDelay batch.

Why a test move drags a source move

swift test at the root builds the WordPressCrossPlatformModules package, which depends only on macOS-clean products. A test can only run there if its subject lives in one of those modules — so each extracted type moves into WordPressShared, gets the members the app touches marked public, and every remaining caller picks up an import WordPressShared. Because WordPress/Classes and Tests/KeystoneTests are file-system-synchronized groups, none of this needs .pbxproj edits.

Sources with user-facing NSLocalizedString were left in place on purpose. Moving translated strings into a module changes their bundle at lookup time and drops them from the app's GlotPress extraction, so candidates like SiteIntentData, ErrorStateViewConfiguration, PluginStore, and MediaSizeSliderCell are excluded here.

Not the Gutenberg processors

An earlier revision of this PR also extracted the Gutenberg content processors into WordPressShared. #25811 landed the same extraction independently — into a dedicated GutenbergProcessors module, with the SwiftSoup 2.13.6 serialization fix — so that work is dropped here to avoid duplicating it. Those suites already run under swift test via GutenbergProcessorsTests. The one exception MediaUploadHashTests (a String.hash guard with no processor dependency, which #25811 left in Keystone) is relocated to WordPressSharedTests here.

Not in this PR

Remaining KeystoneTests candidates each need infrastructure this PR doesn't add, and are follow-ups: a macOS WordPressKitTests root target (unblocks NSAttributedString, SiteSegment, TimeZoneFormatter, Pinghub, StatsPeriodAsyncOperation, the Dashboard view models); resource-bundle support on WordPressSharedTests for fixture-based tests (StockPhotos, SiteSegment, PluginDirectoryEntry); WordPressCore extractions entangled with the feature-flag store; and a new module for the WhatsNew announcement store.

Test plan

• swift test from the repo root: the 12 relocated suites run under the WordPressSharedTests.xctest bundle — 41 tests, 0 failures (part of the full cross-platform run on the rebased branch, alongside trunk's other suites).
• xcodebuild build-for-testing -scheme WordPress against current trunk: ** TEST BUILD SUCCEEDED ** — the app, KeystoneTests, and every Modules/* test target still compile.
• swiftlint --strict: 0 violations across the changed Swift files.
• CI build #33337 confirmed these 12 suites run under WordPressSharedTests in the iOS Unit Tests job and none remain in the WordPressTest (Keystone) bundle (that run predates dropping the Gutenberg commit; the merge queue re-validates the current HEAD).

[wpmobilebot]

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	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	33414
	Version	PR #25815
	Bundle ID	org.wordpress.alpha
	Commit	eb9545f
	Installation URL	2cc9hgh2pusn0

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📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	33414
	Version	PR #25815
	Bundle ID	com.jetpack.alpha
	Commit	eb9545f
	Installation URL	1rkc6290nsb90

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[wpmobilebot]

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