CI: Fix build errors with Xcode 14.3 and platform SDK 13.3

Xcode 14.3 and the macOS 13.3 platform SDK introduced a few breaking
changes:

* Updated AppleClang emits warnings about unqualified std cast calls
  when using C++ - as `move` is too broad a word, developers are to use
  `std::move` to make this explicit. Alas this is exactly what `json11`
  uses and because that library is archived, there is no possibility
  of an upstream update.

* Apple guarded calls to old screen capture APIs as "available but
  deprecated", but seems to have chosen the wrong lower version
  boundary: The calls are flagged as being available for macOS 13 and
  macOS 14 only.

  To fix this, the existing macOS platform SDK header is replaced by a
  local copy that uses macOS 11 as the lower boundary (the oldest macOS
  version supported by obs-studio anyway)