chore: bump MACOSX_DEPLOYMENT_TARGET to 11.0

macOS 10.15 (Catalina) has been EOL for years. Bumping the minimum
deployment target to 11.0 (Big Sur) allows removing legacy fallback
code paths and SYSTEM_VERSION_COMPAT in follow-up commits.

Author: codebytere

binding.gyp

@@ -18,8 +18,7 @@
     ],
     'defines': [ 'NAPI_DISABLE_CPP_EXCEPTIONS' ],
     "xcode_settings": {
-      "MACOSX_DEPLOYMENT_TARGET": "10.15",
-      "SYSTEM_VERSION_COMPAT": 1,
+      "MACOSX_DEPLOYMENT_TARGET": "11.0",
       "OTHER_CPLUSPLUSFLAGS": ["-std=c++20", "-stdlib=libc++"],
       "OTHER_LDFLAGS": [
         "-framework AppKit",