Enable use of `displayException` when generating payload of `InternalError`

[JBetz]

Specifically here:

yesod/yesod-core/src/Yesod/Core/Internal/Run.hs

Line 70 in c9f7ee0

text <- evaluate (T.pack $ show x) `catchAny` \_ ->

The advantage being that you no longer have to use newtypes and Show to produce something human-readable, especially since using Show for pretty printing is becoming more and more of an anti-pattern in Haskell.

It also means that you can take advantage of the work already done by library authors to provide human-readable exceptions. For example: https://github.com/nikita-volkov/hasql/blob/c74c5829c4d3af685c10717b46c73108a9155871/library/Hasql/Errors.hs#L23-L89

[JBetz]

I’ve made an PR but also updated this title to open it up to other solutions.

Perhaps the payload of InternalError should be SomeException rather than Text, so the behaviour can be programmed by redefining the error handler?

[parsonsmatt]

I think I'm inclined to agree that SomeException is preferable here over Text.

[JBetz]

@parsonsmatt I've updated #1869 with the SomeException approach. Are you keen on moving that forward?