feat!(report): generate JSON instead of markdown

This allows us to analyze the report more easily. There is experimental
support for comparing against a base report, but we don't expose that
functionality to the action.

compare.jq

@@ -0,0 +1,20 @@
+# Calculate the change in percentage of a nummeric key
+#
+# Where .[0] is the new value, and .[1] is the old value
+def calc_change($key):
+	. as $input | $input[1][$key] - $input[0][$key];
+
+# Calculate the change in percentage for multiple keys
+#
+# Returns an array of {"key": $key, "value": change%}
+def keys_change_perc($keys):
+	. as $input | $keys | map(. as $key | $input | {"key": $key, "value": . | calc_change($key)});
+
+# For a set of keys, calculate the change percentage and return it as
+# "\($key)Change" = $value in the original object.
+def set_change_perc($keys):
+	. as $input | reduce keys_change_perc($keys)[] as $change ($input[0]; .["\($change.key)Change"] = $change.value);
+
+# Bring everything together
+reduce .[] as $x ({}; . as $acc | reduce ($x | keys[]) as $key ($acc; .[$key] |= . + $x[$key])) |
+	map_values(group_by(.name) | map(set_change_perc(["size", "narSize"])))