feat(hack): add scripts to drive the dev environment headless

Start QEMU in the background with a QMP socket and console logs, take
screenshots, press keys and wait for serial output, so the graphical boot
menu can be driven without a terminal or a window. boot.sh gets opt-in
knobs for this and behaves as before otherwise.

hack/dev/run/key.sh

@@ -0,0 +1,26 @@
+#!/bin/sh
+# Presses keys in the guest, one after another. Join keys with + to press them together.
+# Usage: key.sh <qcode>...   for example: key.sh down down ret   or: key.sh ctrl+alt+delete
+# Environment: KEY_DELAY is seconds between keys (default 0.3).
+set -e
+
+cd "$(dirname "${0}")/../../.." || exit 1
+
+. "hack/dev/run/lib.sh"
+require_running
+
+[ "${#}" -gt 0 ] || die "usage: key.sh <qcode>..."
+
+FIRST=1
+for CHORD in "${@}"; do
+	[ "${FIRST}" = "1" ] || sleep "${KEY_DELAY:-0.3}"
+	FIRST=0
+	KEYS=""
+	OLD_IFS="${IFS}"
+	IFS="+"
+	for KEY in ${CHORD}; do
+		KEYS="${KEYS}${KEYS:+,}{\"type\":\"qcode\",\"data\":\"${KEY}\"}"
+	done
+	IFS="${OLD_IFS}"
+	./hack/dev/run/qmp.sh "{\"execute\":\"send-key\",\"arguments\":{\"keys\":[${KEYS}]}}" >/dev/null
+done