Cleanup various "nil vs empty" confusions in serializaiton of some ObjC types

[beidson]

26b41e6

Cleanup various "nil vs empty" confusions in serializaiton of some ObjC types
rdar://128027011
https://bugs.webkit.org/show_bug.cgi?id=274342

Reviewed by Alex Christensen.

Similar to what I fixed over in https://commits.webkit.org/277627@main, various other ObjC serializers
have some "nil vs empty" confusion that can lead to various wonky side effects.

Let's support the different between nil and empty wherever we can spot it.

* Source/WebKit/Shared/Cocoa/CoreIPCPassKit.h:
(WebKit::CoreIPCPKContact::CoreIPCPKContact):
* Source/WebKit/Shared/Cocoa/CoreIPCPassKit.mm:
(WebKit::CoreIPCPKContact::CoreIPCPKContact):
(WebKit::CoreIPCPKContact::toID const):
* Source/WebKit/Shared/Cocoa/CoreIPCPassKit.serialization.in:

* Source/WebKit/Shared/Cocoa/CoreIPCPersonNameComponents.mm:
(WebKit::CoreIPCPersonNameComponents::toID const):

* Tools/TestWebKitAPI/Tests/IPC/IPCSerialization.mm:
(TEST(IPCSerialization, Basic)):

Canonical link: https://commits.webkit.org/278966@main

6f04da3

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 wincairo-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 wpe-cairo
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🛠 gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2-stress	❌ 🧪 api-gtk
✅ 🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-early-warning-system]

EWS run on current version of this PR (hash 6f04da3)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	✅ 🛠 ios	✅ 🛠 mac	✅ 🛠 wpe	✅ 🛠 wincairo
✅ 🧪 bindings	✅ 🛠 ios-sim	✅ 🛠 mac-AS-debug	✅ 🧪 wpe-wk2	✅ 🧪 wincairo-tests
✅ 🧪 webkitperl	✅ 🧪 ios-wk2	✅ 🧪 api-mac	✅ 🧪 api-wpe
	✅ 🧪 ios-wk2-wpt	✅ 🧪 mac-wk1	✅ 🛠 wpe-cairo
	✅ 🧪 api-ios	✅ 🧪 mac-wk2	✅ 🛠 gtk
	✅ 🛠 tv	✅ 🧪 mac-AS-debug-wk2	✅ 🧪 gtk-wk2
	✅ 🛠 tv-sim	✅ 🧪 mac-wk2-stress	❌ 🧪 api-gtk
✅ 🛠 🧪 merge	✅ 🛠 watch
	✅ 🛠 watch-sim

[webkit-commit-queue]

Committed 278966@main (26b41e6): https://commits.webkit.org/278966@main

Reviewed commits have been landed. Closing PR #28747 and removing active labels.