Move the event mask into a platform-neutral product

`InotifyEventMask` took its bits from the C header, so nothing that
imported it could build outside Linux. The new `InotifyMask` product
spells out the kernel constants instead; a Linux test compares each
of them with the header. `Inotify` re-exports the module, so
existing code is unaffected.

Tests/InotifyIntegrationTests/EventMaskTests.swift

@@ -0,0 +1,31 @@
+import CInotify
+import Testing
+@testable import Inotify
+
+@Suite("Event Mask")
+struct EventMaskTests {
+	@Test(arguments: [
+		(InotifyEventMask.access, UInt32(IN_ACCESS)),
+		(.attrib, UInt32(IN_ATTRIB)),
+		(.closeWrite, UInt32(IN_CLOSE_WRITE)),
+		(.closeNoWrite, UInt32(IN_CLOSE_NOWRITE)),
+		(.create, UInt32(IN_CREATE)),
+		(.delete, UInt32(IN_DELETE)),
+		(.deleteSelf, UInt32(IN_DELETE_SELF)),
+		(.modify, UInt32(IN_MODIFY)),
+		(.moveSelf, UInt32(IN_MOVE_SELF)),
+		(.movedFrom, UInt32(IN_MOVED_FROM)),
+		(.movedTo, UInt32(IN_MOVED_TO)),
+		(.open, UInt32(IN_OPEN)),
+		(.dontFollow, UInt32(IN_DONT_FOLLOW)),
+		(.onlyDir, UInt32(IN_ONLYDIR)),
+		(.oneShot, UInt32(IN_ONESHOT)),
+		(.isDir, UInt32(IN_ISDIR)),
+		(.ignored, UInt32(IN_IGNORED)),
+		(.queueOverflow, UInt32(IN_Q_OVERFLOW)),
+		(.unmount, UInt32(IN_UNMOUNT)),
+	] as [(InotifyEventMask, UInt32)])
+	func matchesTheKernelConstant(mask: InotifyEventMask, constant: UInt32) {
+		#expect(mask.rawValue == constant)
+	}
+}