Increase minimum macOS SDK from 10.13 to 10.14

Increases the minimum macOS SDK and the macOS deployment target from
10.13 to 10.14.

Also enables aligned allocations on macOS. We previously set
`-fno-aligned-allocation` on macOS since it was unsupported for arm64
prior to macOS 10.14.

Issue: flutter/flutter#114445

build/config/compiler/BUILD.gn

@@ -176,11 +176,6 @@ config("compiler") {
         "-arch",
         "arm64",
       ]
-      if (is_mac) {
-        # Aligned allocations are only supported on arm64 after macOS 10.14,
-        # however our deployment target is currently 10.11.
-        common_mac_flags += [ "-fno-aligned-allocation" ]
-      }
     }
 
     cflags += common_mac_flags

build/config/mac/mac_sdk.gni

@@ -6,11 +6,11 @@ import("//build/toolchain/goma.gni")
 
 declare_args() {
   # Minimum supported version of the Mac SDK.
-  mac_sdk_min = "10.13"
+  mac_sdk_min = "10.14"
 
   # The MACOSX_DEPLOYMENT_TARGET variable used when compiling.
   # Must be of the form x.x.x for Info.plist files.
-  mac_deployment_target = "10.13.0"
+  mac_deployment_target = "10.14.0"
 
   # Path to a specific version of the Mac SDK, not including a backslash at
   # the end. If empty, the path to the lowest version greater than or equal to