Update macOS Xcode compatibilityVersion (#71745)

diff --git a/dev/benchmarks/macrobenchmarks/macos/Runner.xcodeproj/project.pbxproj b/dev/benchmarks/macrobenchmarks/macos/Runner.xcodeproj/project.pbxproj
index 9a82f9b..2817159 100644
--- a/dev/benchmarks/macrobenchmarks/macos/Runner.xcodeproj/project.pbxproj
+++ b/dev/benchmarks/macrobenchmarks/macos/Runner.xcodeproj/project.pbxproj

@@ -211,7 +211,7 @@
 				};
 			};
 			buildConfigurationList = 33CC10E82044A3C60003C045 /* Build configuration list for PBXProject "Runner" */;
-			compatibilityVersion = "Xcode 8.0";
+			compatibilityVersion = "Xcode 9.3";
 			developmentRegion = en;
 			hasScannedForEncodings = 0;
 			knownRegions = (

diff --git a/dev/integration_tests/flutter_gallery/macos/Runner.xcodeproj/project.pbxproj b/dev/integration_tests/flutter_gallery/macos/Runner.xcodeproj/project.pbxproj
index 5586e24..9799047 100644
--- a/dev/integration_tests/flutter_gallery/macos/Runner.xcodeproj/project.pbxproj
+++ b/dev/integration_tests/flutter_gallery/macos/Runner.xcodeproj/project.pbxproj

@@ -235,7 +235,7 @@
 				};
 			};
 			buildConfigurationList = 33CC10E82044A3C60003C045 /* Build configuration list for PBXProject "Runner" */;
-			compatibilityVersion = "Xcode 8.0";
+			compatibilityVersion = "Xcode 9.3";
 			developmentRegion = en;
 			hasScannedForEncodings = 0;
 			knownRegions = (

diff --git a/dev/integration_tests/ui/macos/Runner.xcodeproj/project.pbxproj b/dev/integration_tests/ui/macos/Runner.xcodeproj/project.pbxproj
index 8c618fd..de8844b 100644
--- a/dev/integration_tests/ui/macos/Runner.xcodeproj/project.pbxproj
+++ b/dev/integration_tests/ui/macos/Runner.xcodeproj/project.pbxproj

@@ -214,7 +214,7 @@
 				};
 			};
 			buildConfigurationList = 33CC10E82044A3C60003C045 /* Build configuration list for PBXProject "Runner" */;
-			compatibilityVersion = "Xcode 8.0";
+			compatibilityVersion = "Xcode 9.3";
 			developmentRegion = en;
 			hasScannedForEncodings = 0;
 			knownRegions = (

diff --git a/dev/manual_tests/macos/Runner.xcodeproj/project.pbxproj b/dev/manual_tests/macos/Runner.xcodeproj/project.pbxproj
index aef5c68..9cfacde 100644
--- a/dev/manual_tests/macos/Runner.xcodeproj/project.pbxproj
+++ b/dev/manual_tests/macos/Runner.xcodeproj/project.pbxproj

@@ -214,7 +214,7 @@
 				};
 			};
 			buildConfigurationList = 33CC10E82044A3C60003C045 /* Build configuration list for PBXProject "Runner" */;
-			compatibilityVersion = "Xcode 8.0";
+			compatibilityVersion = "Xcode 9.3";
 			developmentRegion = en;
 			hasScannedForEncodings = 0;
 			knownRegions = (

diff --git a/packages/flutter_tools/templates/app/macos.tmpl/Runner.xcodeproj/project.pbxproj.tmpl b/packages/flutter_tools/templates/app/macos.tmpl/Runner.xcodeproj/project.pbxproj.tmpl
index 8ed53e8..f88fac8 100644
--- a/packages/flutter_tools/templates/app/macos.tmpl/Runner.xcodeproj/project.pbxproj.tmpl
+++ b/packages/flutter_tools/templates/app/macos.tmpl/Runner.xcodeproj/project.pbxproj.tmpl

@@ -214,7 +214,7 @@
 				};
 			};
 			buildConfigurationList = 33CC10E82044A3C60003C045 /* Build configuration list for PBXProject "Runner" */;
-			compatibilityVersion = "Xcode 8.0";
+			compatibilityVersion = "Xcode 9.3";
 			developmentRegion = en;
 			hasScannedForEncodings = 0;
 			knownRegions = (

diff --git a/packages/integration_test/example/macos/Runner.xcodeproj/project.pbxproj b/packages/integration_test/example/macos/Runner.xcodeproj/project.pbxproj
index 718462e..8cb543b 100644
--- a/packages/integration_test/example/macos/Runner.xcodeproj/project.pbxproj
+++ b/packages/integration_test/example/macos/Runner.xcodeproj/project.pbxproj

@@ -234,7 +234,7 @@
 				};
 			};
 			buildConfigurationList = 33CC10E82044A3C60003C045 /* Build configuration list for PBXProject "Runner" */;
-			compatibilityVersion = "Xcode 8.0";
+			compatibilityVersion = "Xcode 9.3";
 			developmentRegion = en;
 			hasScannedForEncodings = 0;
 			knownRegions = (