[macOS Ventura] Support building open source WebKit

[Patrick Angle]

macOS Ventura Beta 3 (22A5295h) /w Xcode 14 beta 3 (14A5270f) with top-of-tree checkout.

Using either `make` or `build-webkit` I'm getting the errors like this when trying to build:
```
In file included from /Users/patrickangle/Developer/WebKit/Source/WebCore/PAL/pal/cocoa/VisionKitCoreSoftLink.mm:30:
/Users/patrickangle/Developer/WebKit/WebKitBuild/Release/usr/local/include/pal/spi/cocoa/VisionKitCoreSPI.h:160:40: error: pointer is missing a nullability type specifier (_Nonnull, _Nullable, or _Null_unspecified) [-Werror,-Wnullability-completeness]
```

If I NS_ASSUME_NONNULL_BEGIN all the things, I then fail with:
```
In file included from /Users/patrickangle/Developer/WebKit/Source/WebCore/PAL/pal/cocoa/VisionKitCoreSoftLink.mm:30:
/Users/patrickangle/Developer/WebKit/WebKitBuild/Release/usr/local/include/pal/spi/cocoa/VisionKitCoreSPI.h:171:12: error: cannot find interface declaration for 'VKCImageAnalysis'; did you mean 'VKImageAnalysis'?
@interface VKCImageAnalysis (Staging_93280734)
/Users/patrickangle/Developer/WebKit/WebKitBuild/Release/usr/local/include/pal/spi/cocoa/VisionKitCoreSPI.h:87:12: note: 'VKImageAnalysis' declared here
@interface VKImageAnalysis : NSObject <NSSecureCoding>
/Users/patrickangle/Developer/WebKit/Source/WebCore/PAL/pal/cocoa/VisionKitCoreSoftLink.mm:42:72: error: declaration of 'vk_cgImageRemoveBackground' has a different language linkage
SOFT_LINK_FUNCTION_MAY_FAIL_FOR_SOURCE_WITH_EXPORT(PAL, VisionKitCore, vk_cgImageRemoveBackground, void, (CGImageRef image, BOOL crop, VKCGImageRemoveBackgroundCompletion completion), (image, crop, completion), PAL_EXPORT)
In file included from /Users/patrickangle/Developer/WebKit/Source/WebCore/PAL/pal/cocoa/VisionKitCoreSoftLink.mm:30:
/Users/patrickangle/Developer/WebKit/WebKitBuild/Release/usr/local/include/pal/spi/cocoa/VisionKitCoreSPI.h:192:13: note: previous declaration is here
extern void vk_cgImageRemoveBackground(CGImageRef, BOOL cropToFit, VKCGImageRemoveBackgroundCompletion);
/Users/patrickangle/Developer/WebKit/Source/WebCore/PAL/pal/cocoa/VisionKitCoreSoftLink.mm:43:72: error: declaration of 'vk_cgImageRemoveBackgroundWithDownsizing' has a different language linkage
SOFT_LINK_FUNCTION_MAY_FAIL_FOR_SOURCE_WITH_EXPORT(PAL, VisionKitCore, vk_cgImageRemoveBackgroundWithDownsizing, void, (CGImageRef image, BOOL canDownsize, BOOL cropToFit, void(^completion)(CGImageRef, NSError *)), (image, canDownsize, cropToFit, completion), PAL_EXPORT)
In file included from /Users/patrickangle/Developer/WebKit/Source/WebCore/PAL/pal/cocoa/VisionKitCoreSoftLink.mm:30:
/Users/patrickangle/Developer/WebKit/WebKitBuild/Release/usr/local/include/pal/spi/cocoa/VisionKitCoreSPI.h:193:13: note: previous declaration is here
extern void vk_cgImageRemoveBackgroundWithDownsizing(CGImageRef, BOOL canDownsize, BOOL cropToFit, void(^completion)(CGImageRef, NSError *));
```

[Patrick Angle]

I tried taking a stab at fixing this, but even if just my blanket use of NS_ASSUME_NONNULL_BEGIN had fixed the build someone more familiar with these APIs would probably have had to actually help get the nullable annotations to be accurate.

[Radar WebKit Bug Importer]

<rdar://problem/96715188>

[Alexey Proskuryakov]

*** This bug has been marked as a duplicate of bug 242429 ***