Add `clojure.lang.ExceptionInfo`'s `ex-data` where available

[devurandom]

prone.stacks/normalize-exception, via prone.stacks/add-data sets a clojure.lang.ExceptionInfo's ex-data as :data on the normalized exception. This data is generally useful, so pass it on to Sentry via the mechanism.data key of the exception payload:

• https://develop.sentry.dev/sdk/event-payloads/exception/#exception-mechanism

Since Sentry does not support nested maps (it will not display the data at all in that case), we flatten the data using pr-str.