Refactor and improve ErrorState::Dump

[kinkie]

Rework the internals for generating output in ErrorState::Dump,
used for expanding the '%W' token in error page templates.

Also fix a bug with excessive html-quoting of the output.

[kinkie]

Run-tested. Output:

?subject=CacheErrorInfo%20-%20ERR_ACCESS_DENIED**&**body=CacheHost%3A%20n2%0D%0AErrPage%3A%20ERR_ACCESS_DENIED%0D%0AErr%3A%20%5Bnone%5D%0D%0ATimeStamp%3A%20Sat%2C%2009%20Mar%202024%2014%3A48%3A00%20GMT%0D%0AClientIP%3A%20127.0.0.1%3A53002%0D%0A%0D%0AHTTP%20Request%3A%0D%0AGET%20%2Fbar%20HTTP%2F1.1%0D%0AHost%3A%20www.fb.com%0D%0AUser-Agent%3A%20curl%2F7.81.0%0D%0AAccept%3A%20%2A%2F%2A%0D%0AProxy-Connection%3A%20Keep-Alive%0D%0A%0D%0A%0D%0A

In bold is a bug (&amp should be &).
That bug is not new, master has the same faulty behaviour

[rousskov]

Run-tested. Output: [%W value]

Please post two %W values: one before and one after these changes. Do not use text formatting. Do use diff quoting format to improve readability:

   ```diff
   - before
   + after 
   `` `

If you do it right, you will see GitHub rendering your diff as a diff in Preview, like here:

- before
+ after

(&amp should be &). That bug is not new, master has the same faulty behaviour

Are you preserving the old bug because it is difficult to fix or for some other reason? If it is difficult to fix, can you mark the buggy code with an XXX C++ comment?

[yadij]

?subject=CacheErrorInfo%20-%20ERR_ACCESS_DENIED**&**body=CacheHost%3A%20n2%0D%0AErrPage

In bold is a bug (&amp should be &). That bug is not new, master has the same faulty behaviour

IIRC this string is being generated for a mailto:admin@example.com?subject=...&body=... URL query-string. The particular & you have marked in bold is the query-string delimiter which should not be URL-encoded.

[yadij]

LGTM, just Alex review items to resolve.

[kinkie]

The particular & you have marked in bold is the query-string delimiter which should not be URL-encoded.

Yes; it's mostly a note to self, I haven't had the time to investigate where that url-encoding is taking place

[rousskov]

This new/PR code is implicitly using Ip::Address::toUrl(). Official code uses Ip::Address::toStr(). The two methods produce different output. If this change is desirable, please disclose it (with its rationale and effect) in the PR description. Otherwise, refactor to avoid an undesirable change.

[kinkie]

Thanks for picking this up; reverted to the previous output

[yadij]

This change is still present. Only change was the line it occurs on - which confuses github into marking it "outdated".

Thank you for addressing my change requests.