Xcode: Use explicitFileType to mark source types (#14093)

Replace use of lastKnownFileType with explicitFileType to insist
that Xcode treat the file as we ask.

Modules/CompilerId/Xcode-1.pbxproj.in

@@ -56,7 +56,7 @@
 		2C18F0B415DC1DC700593670 = {
 			fileEncoding = 30;
 			isa = PBXFileReference;
-			lastKnownFileType = @id_type@;
+			explicitFileType = @id_type@;
 			path = @id_src@;
 			refType = 4;
 			sourceTree = "<group>";

Modules/CompilerId/Xcode-2.pbxproj.in

@@ -7,7 +7,7 @@
 	objects = {
 
 		2C18F0B615DC1E0300593670 = {isa = PBXBuildFile; fileRef = 2C18F0B415DC1DC700593670; };
-		2C18F0B415DC1DC700593670 = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = @id_type@; path = @id_src@; sourceTree = "<group>"; };
+		2C18F0B415DC1DC700593670 = {isa = PBXFileReference; fileEncoding = 4; explicitFileType = @id_type@; path = @id_src@; sourceTree = "<group>"; };
 		8DD76F6C0486A84900D96B5E = {isa = PBXFileReference; explicitFileType = "compiled.mach-o.executable"; includeInIndex = 0; path = CompilerId@id_lang@; sourceTree = BUILT_PRODUCTS_DIR; };
 
 		08FB7794FE84155DC02AAC07 = {

Modules/CompilerId/Xcode-3.pbxproj.in

@@ -7,7 +7,7 @@
 	objects = {
 
 		2C18F0B615DC1E0300593670 = {isa = PBXBuildFile; fileRef = 2C18F0B415DC1DC700593670; };
-		2C18F0B415DC1DC700593670 = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = @id_type@; path = @id_src@; sourceTree = "<group>"; };
+		2C18F0B415DC1DC700593670 = {isa = PBXFileReference; fileEncoding = 4; explicitFileType = @id_type@; path = @id_src@; sourceTree = "<group>"; };
 		08FB7794FE84155DC02AAC07 = {
 			isa = PBXGroup;
 			children = (

Source/cmGlobalXCodeGenerator.cxx

@@ -839,7 +839,7 @@ GetSourcecodeValueFromFileExtension(const std::string& _ext,
   //  // Already specialized above or we leave sourcecode == "sourcecode"
   //  // which is probably the most correct choice. Extensionless headers,
   //  // for example... Or file types unknown to Xcode that do not map to a
-  //  // valid lastKnownFileType value.
+  //  // valid explicitFileType value.
   //  }
 
   return sourcecode;
@@ -882,7 +882,7 @@ cmGlobalXCodeGenerator::CreateXCodeFileReferenceFromPath(
 
   std::string sourcecode = GetSourcecodeValueFromFileExtension(ext, lang);
 
-  fileRef->AddAttribute("lastKnownFileType",
+  fileRef->AddAttribute("explicitFileType",
                         this->CreateString(sourcecode.c_str()));
 
   // Store the file path relative to the top of the source tree.
@@ -1003,7 +1003,7 @@ cmGlobalXCodeGenerator::CreateXCodeTargets(cmLocalGenerator* gen,
                                     *i, cmtarget);
       cmXCodeObject* fr = xsf->GetObject("fileRef");
       cmXCodeObject* filetype =
-        fr->GetObject()->GetObject("lastKnownFileType");
+        fr->GetObject()->GetObject("explicitFileType");
 
       cmTarget::SourceFileFlags tsFlags =
         cmtarget.GetTargetSourceFileFlags(*i);