vrt: Fail the transaction for all out of workspace conditions

[dridi]

See #3765 (comment).

Most VRT functions to convert VCL types to STRING ignore workspace overflows. If they failed, that would become very problematic in vcl_synth where even static assignments of headers would simply fail. This is handled in #3768, and this ticket is here to make sure we review workspace usage in VRT and maybe fail where we currently don't (or document in the code why we wouldn't).

[dridi]

I initially didn't see the link between this ticket and #3825, but the two should be linked. Both are very broad, and there is some overlap, but #3825 is sort of equivalent for all http_*() failures and not limited to workspace overflows.