Log like a debug build on macOS, where a Mac user can find it

Nobody working on DarkRoom has a Mac, so every macOS build is in the hands
of someone who can send a log and cannot attach a debugger. Three changes
make that log worth sending:

- The desktop's default filter on macOS is `debug` for every `dr_*` crate,
  the desktop crate and `onnxruntime` (the runtime's own session log).
- The state directory — the log and crash records — is `~/Library/Logs`
  on macOS rather than the `~/.local/state` Finder hides; Console.app
  lists it. Config and data keep the Unix rules.
- A `diagnostic` cargo profile: release plus line tables, so a crash
  record's backtrace reads file:line. On macOS the tables are in the
  `.dSYM` beside the executable, which the bundle must keep.

platform/dr-plat/src/diagnostics.rs

@@ -46,6 +46,8 @@
 //!
 //! * Linux: `$XDG_STATE_HOME/darkroom/darkroom.log`, else
 //!   `~/.local/state/darkroom/darkroom.log`.
+//! * macOS: `$XDG_STATE_HOME/darkroom/darkroom.log`, else
+//!   `~/Library/Logs/darkroom/darkroom.log`, where Console.app lists it.
 //! * Android: `/sdcard/Android/data/paris.tourolle.darkroom/files/darkroom.log`,
 //!   which `adb pull` reads from an ordinary release build. See
 //!   [`crate::state`] for why not the internal directory, and