Merge pull request swiftlang#79720 from AnthonyLatsis/haliotis-rufescens

[NFC] test: Factor out feature frontend tests into subdirectory

Author: AnthonyLatsis

test/Frontend/experimental-features-asserts.swift renamed to test/Frontend/features/experimental-features-asserts.swift

@@ -13,10 +13,10 @@ import sys
 # they cannot automatically be checked.
 EXCEPTIONAL_FILES = [
     # Tests for ParserValidation not being defined in no-asserts compilers
-    pathlib.Path("test/Frontend/experimental-features-no-asserts.swift"),
+    pathlib.Path("test/Frontend/features/experimental-features-no-asserts.swift"),
     # Tests for UnknownFeature not existing
-    pathlib.Path("test/Frontend/upcoming_feature.swift"),
-    pathlib.Path("test/Frontend/strict_features.swift"),
+    pathlib.Path("test/Frontend/features/upcoming_feature.swift"),
+    pathlib.Path("test/Frontend/features/strict_features.swift"),
     # Tests for ModuleInterfaceExportAs being ignored
     pathlib.Path("test/ModuleInterface/swift-export-as.swift"),
     # Uses the pseudo-feature AvailabilityMacro=