dev: check version of bash on startup (#12204)

If you are using an old version of bash our dev scripts fails in subtle
ways. For example we will detect file changes, but recompilation will
fail. This check ensures a dev is on version 5 of bash. If not it
fails the script and informs them how to upgrade.

dev/start.sh

@@ -2,6 +2,13 @@
 
 set -euf -o pipefail
 
+if [[ ${BASH_VERSION:0:1} -lt 5 ]]; then
+  echo "Please upgrade bash to version 5. Currently on ${BASH_VERSION}."
+  echo
+  echo "  brew install bash"
+  exit 1
+fi
+
 unset CDPATH
 cd "$(dirname "${BASH_SOURCE[0]}")/.." # cd to repo root dir