build: make gomobile iOS build to .xcframework folder

Recent gomobile versions are now building for the `xcframework`
packaging format instead of `framework`. This commit addresses
this by outputting to a `.xcframework` folder.

Makefile

@@ -22,7 +22,7 @@ GOFUZZ_BIN := $(GO_BIN)/go-fuzz
 
 MOBILE_BUILD_DIR :=${GOPATH}/src/$(MOBILE_PKG)/build
 IOS_BUILD_DIR := $(MOBILE_BUILD_DIR)/ios
-IOS_BUILD := $(IOS_BUILD_DIR)/Lndmobile.framework
+IOS_BUILD := $(IOS_BUILD_DIR)/Lndmobile.xcframework
 ANDROID_BUILD_DIR := $(MOBILE_BUILD_DIR)/android
 ANDROID_BUILD := $(ANDROID_BUILD_DIR)/Lndmobile.aar