Stackwalker is misconfigured to downloads symbols from symbol servers

See https://forum.unity.com/threads/unity-2022-1-9f1c1-windows-non-development-standalone-player-insists-downloading-debug-symbols.1309950/

This causes the player to hang the first time a full stacktrace is needed if the PDBs aren't cached locally (even in non-development builds!). We should disable the symbol downloading functionality.