Follow-up to "[visionOS] Add SPI module for LinearMediaKit"

rdar://127327242
https://bugs.webkit.org/show_bug.cgi?id=273527

Unreviewed.

Minor changes I forgot to include in the original commit.

* Source/WebKit/Configurations/WebKitSwift.xcconfig: Building visionOS
  with the public SDK requires import XPCSPI.h, which assumes a c++
  compiler. Rather than fix that header to be language-agnostic, enable
  c++ interop mode, since WebKitSwift will need it eventually
  regardless.
* Source/WebKit/WebKit.xcodeproj/project.pbxproj: Track the
  LinearMediaKit.swiftinterface file in the project.

Canonical link: https://commits.webkit.org/278269@main

Source/WebKit/Configurations/WebKitSwift.xcconfig

@@ -54,6 +54,7 @@ WK_EXCLUDED_TEXT_STYLE_MANAGER_FILES_ = TextStyleManager.swift
 EXCLUDED_SOURCE_FILE_NAMES = $(WK_EXCLUDED_COORDINATOR_FILES) $(WK_EXCLUDED_MARKETPLACE_KIT_WRAPPER_FILES) $(WK_EXCLUDED_TEXT_EXTRACTION_FILES) $(EXCLUDED_IOS_RESOURCE_FILE_NAMES) $(EXCLUDED_MACOS_PLUGIN_FILE_NAMES) $(WK_EXCLUDED_TEXT_STYLE_MANAGER_FILES)
 
 SWIFT_INSTALL_OBJC_HEADER = NO
+SWIFT_OBJC_INTEROP_MODE = objcxx;
 SWIFT_VERSION = 5.0;
 
 CLANG_INSTRUMENT_FOR_OPTIMIZATION_PROFILING = NO; // Disable PGO profile generation

Source/WebKit/WebKit.xcodeproj/project.pbxproj

@@ -7919,6 +7919,7 @@
 		D952EC7D289C9A4C006C240A /* WebPermissionControllerProxyMessageReceiver.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = WebPermissionControllerProxyMessageReceiver.cpp; sourceTree = "<group>"; };
 		DA97E4AC2B6BCCF20009E90B /* WebExtension.serialization.in */ = {isa = PBXFileReference; lastKnownFileType = text; name = WebExtension.serialization.in; path = UIProcess/Extensions/WebExtension.serialization.in; sourceTree = "<group>"; };
 		DD284681291F7CEF0009A61D /* APIFeatureStatus.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = APIFeatureStatus.h; sourceTree = "<group>"; };
+		DD6E58C52BE070850000C264 /* LinearMediaKit.swiftinterface */ = {isa = PBXFileReference; lastKnownFileType = text; path = LinearMediaKit.swiftinterface; sourceTree = "<group>"; };
 		DD8CD35F296D03A300C04CA1 /* _WKFeature.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = _WKFeature.mm; sourceTree = "<group>"; };
 		DD8CD360296D03A300C04CA1 /* _WKFeature.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = _WKFeature.h; sourceTree = "<group>"; };
 		DD8CD361296D03A400C04CA1 /* _WKFeatureInternal.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = _WKFeatureInternal.h; sourceTree = "<group>"; };
@@ -15720,6 +15721,7 @@
 		E5BF52E02A44A5D9005B2848 /* visionos */ = {
 			isa = PBXGroup;
 			children = (
+				DD6E58C52BE070850000C264 /* LinearMediaKit.swiftinterface */,
 				E539DFEA2A44A69100769F09 /* MRUIKitSPI.h */,
 				E539DFEC2A44A78600769F09 /* RealitySimulationServicesSPI.h */,
 			);