ios [nfc]: Rename AppDelegate.mm from ….m, following template

I opened the file in Xcode, used "Navigate > Reveal in Project Navigator",
and then long-clicked it there to get a UI to rename the file.
That moved the file itself, and made these small changes in the
Xcode project file.

This follows a change in the template app on the way to RN v0.68:
  facebook/react-native@4fb49cd55 Rename AppDelegate.m to AppDelegate.mm in the app template

which was done as preparation for the New Arch-related changes we'll
follow next.  That commit has a bunch of additional churn and new mess
in the Xcode project file, which apparently Xcode did automatically
when that change's author tried opening the project; but happily that
didn't happen for me.

Author: gnprice

ios/ZulipMobile.xcodeproj/project.pbxproj

@@ -7,7 +7,7 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
-		13B07FBC1A68108700A75B9A /* AppDelegate.m in Sources */ = {isa = PBXBuildFile; fileRef = 13B07FB01A68108700A75B9A /* AppDelegate.m */; };
+		13B07FBC1A68108700A75B9A /* AppDelegate.mm in Sources */ = {isa = PBXBuildFile; fileRef = 13B07FB01A68108700A75B9A /* AppDelegate.mm */; };
 		13B07FBF1A68108700A75B9A /* Assets.xcassets in Resources */ = {isa = PBXBuildFile; fileRef = 13B07FB51A68108700A75B9A /* Assets.xcassets */; };
 		13B07FC11A68108700A75B9A /* main.m in Sources */ = {isa = PBXBuildFile; fileRef = 13B07FB71A68108700A75B9A /* main.m */; };
 		42689E9C23466FF7007540AA /* webview in Resources */ = {isa = PBXBuildFile; fileRef = 42689E9B23466FF7007540AA /* webview */; };
@@ -24,7 +24,7 @@
 /* Begin PBXFileReference section */
 		13B07F961A680F5B00A75B9A /* ZulipMobile.app */ = {isa = PBXFileReference; explicitFileType = wrapper.application; includeInIndex = 0; path = ZulipMobile.app; sourceTree = BUILT_PRODUCTS_DIR; };
 		13B07FAF1A68108700A75B9A /* AppDelegate.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = AppDelegate.h; path = ZulipMobile/AppDelegate.h; sourceTree = "<group>"; };
-		13B07FB01A68108700A75B9A /* AppDelegate.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; name = AppDelegate.m; path = ZulipMobile/AppDelegate.m; sourceTree = "<group>"; };
+		13B07FB01A68108700A75B9A /* AppDelegate.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; name = AppDelegate.mm; path = ZulipMobile/AppDelegate.mm; sourceTree = "<group>"; };
 		13B07FB51A68108700A75B9A /* Assets.xcassets */ = {isa = PBXFileReference; lastKnownFileType = folder.assetcatalog; name = Assets.xcassets; path = ZulipMobile/Assets.xcassets; sourceTree = "<group>"; };
 		13B07FB61A68108700A75B9A /* Info.plist */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.plist.xml; name = Info.plist; path = ZulipMobile/Info.plist; sourceTree = "<group>"; };
 		13B07FB71A68108700A75B9A /* main.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; name = main.m; path = ZulipMobile/main.m; sourceTree = "<group>"; };
@@ -65,7 +65,7 @@
 				8BEA1EEE24A6983D00674040 /* ZLPConstants.m */,
 				3C4249EC1EF6E16500D245F1 /* ZulipMobile.entitlements */,
 				13B07FAF1A68108700A75B9A /* AppDelegate.h */,
-				13B07FB01A68108700A75B9A /* AppDelegate.m */,
+				13B07FB01A68108700A75B9A /* AppDelegate.mm */,
 				13B07FB51A68108700A75B9A /* Assets.xcassets */,
 				13B07FB61A68108700A75B9A /* Info.plist */,
 				3787526927F5503200B81DB8 /* zulip-icons.ttf */,
@@ -368,7 +368,7 @@
 			files = (
 				CFA67D201EC23BCB0070048E /* UtilManager.m in Sources */,
 				8BEA1EF024A6983D00674040 /* ZLPConstants.m in Sources */,
-				13B07FBC1A68108700A75B9A /* AppDelegate.m in Sources */,
+				13B07FBC1A68108700A75B9A /* AppDelegate.mm in Sources */,
 				13B07FC11A68108700A75B9A /* main.m in Sources */,
 				A65C1ECEE03CA6692FC807AA /* ExpoModulesProvider.swift in Sources */,
 			);