Use copts instead of swift_version attr

swift_version attr is being deprecated in favor of:
1) Explicitly specifying via flag in copts attr
2) Using the default value for the active Xcode

PiperOrigin-RevId: 188345409

src/TulsiGeneratorIntegrationTests/Resources/GoldenProjects/SwiftProject.xcodeproj/project.pbxproj

diff --git a/src/TulsiGeneratorIntegrationTests/Resources/GoldenProjects/SwiftProject.xcodeproj/project.pbxproj b/src/TulsiGeneratorIntegrationTests/Resources/GoldenProjects/SwiftProject.xcodeproj/project.pbxproj
index c4f7326..3629c02 100644
--- a/src/TulsiGeneratorIntegrationTests/Resources/GoldenProjects/SwiftProject.xcodeproj/project.pbxproj
+++ b/src/TulsiGeneratorIntegrationTests/Resources/GoldenProjects/SwiftProject.xcodeproj/project.pbxproj
@@ -383,6 +383,7 @@
 				GCC_PREPROCESSOR_DEFINITIONS = "DEBUG=1";
 				HEADER_SEARCH_PATHS = "$(inherited) $(TULSI_BWRS)/tools/cpp/gcc3 ";
 				IPHONEOS_DEPLOYMENT_TARGET = 8.0;
+				OTHER_CFLAGS = "-swift-version 3";
 				PRODUCT_NAME = _idx_SwiftLibraryV3_56AA3A57_ios_min8.0;
 				SDKROOT = iphoneos;
 				SWIFT_INCLUDE_PATHS = "$(inherited) $(TULSI_BWRS)/_tulsi-includes/x/x/tulsi_e2e_swift/SwiftLibraryV3/_objs";
@@ -395,6 +396,7 @@
 				GCC_PREPROCESSOR_DEFINITIONS = "DEBUG=1";
 				HEADER_SEARCH_PATHS = "$(inherited) $(TULSI_BWRS)/tools/cpp/gcc3 ";
 				IPHONEOS_DEPLOYMENT_TARGET = 8.0;
+				OTHER_CFLAGS = "-swift-version 4";
 				PRODUCT_NAME = _idx_SwiftLibraryV4_56AA3A59_ios_min8.0;
 				SDKROOT = iphoneos;
 				SWIFT_INCLUDE_PATHS = "$(inherited) $(TULSI_BWRS)/_tulsi-includes/x/x/tulsi_e2e_swift/SwiftLibraryV4/_objs";
@@ -473,6 +475,7 @@
 				GCC_PREPROCESSOR_DEFINITIONS = "NDEBUG=1";
 				HEADER_SEARCH_PATHS = "$(inherited) $(TULSI_BWRS)/tools/cpp/gcc3 ";
 				IPHONEOS_DEPLOYMENT_TARGET = 8.0;
+				OTHER_CFLAGS = "-swift-version 3";
 				PRODUCT_NAME = _idx_SwiftLibraryV3_56AA3A57_ios_min8.0;
 				SDKROOT = iphoneos;
 				SWIFT_INCLUDE_PATHS = "$(inherited) $(TULSI_BWRS)/_tulsi-includes/x/x/tulsi_e2e_swift/SwiftLibraryV3/_objs";
@@ -485,6 +488,7 @@
 				GCC_PREPROCESSOR_DEFINITIONS = "NDEBUG=1";
 				HEADER_SEARCH_PATHS = "$(inherited) $(TULSI_BWRS)/tools/cpp/gcc3 ";
 				IPHONEOS_DEPLOYMENT_TARGET = 8.0;
+				OTHER_CFLAGS = "-swift-version 4";
 				PRODUCT_NAME = _idx_SwiftLibraryV4_56AA3A59_ios_min8.0;
 				SDKROOT = iphoneos;
 				SWIFT_INCLUDE_PATHS = "$(inherited) $(TULSI_BWRS)/_tulsi-includes/x/x/tulsi_e2e_swift/SwiftLibraryV4/_objs";

src/TulsiGeneratorIntegrationTests/Resources/Swift.BUILD

diff --git a/src/TulsiGeneratorIntegrationTests/Resources/Swift.BUILD b/src/TulsiGeneratorIntegrationTests/Resources/Swift.BUILD
index 6c41955..f2851b9 100644
--- a/src/TulsiGeneratorIntegrationTests/Resources/Swift.BUILD
+++ b/src/TulsiGeneratorIntegrationTests/Resources/Swift.BUILD
@@ -50,7 +50,10 @@
         "SwiftLibraryV3/srcs/a.swift",
         "SwiftLibraryV3/srcs/b.swift",
     ],
-    swift_version = 3,
+    copts = [
+        "-swift-version",
+        "3",
+    ],
 )
 
 swift_library(
@@ -59,7 +62,10 @@
         "SwiftLibraryV4/srcs/a.swift",
         "SwiftLibraryV4/srcs/b.swift",
     ],
-    swift_version = 4,
+    copts = [
+        "-swift-version",
+        "4",
+    ],
 )
 
 swift_library(