This includes building the fuzzer to avoid code rot, but exercising
the fuzzer will be done elsewhere.

As WS_Reset() clears the overflow marker, the correct order for
resetting and marking an overflow is WS_Reset(); WS_MarkOverflow();

Fixes the last seemingly obscure bit of #2645

Conflicts:
	doc/sphinx/reference/vcl_var.rst (beresp.filters)

list of VCLs" vs. "Do things with VCLs on list"

Ref: #2645

Should we plan to phase out synthetic() ?

Thank you to @martin-uplex for the review

Conflicts:
	bin/varnishd/cache/cache.h

Arguably, this is a breaking change in $ABI vrt.

Supress terminal responses by default and hope they look right.

Return HTC_S_OVERFLOW if exceeded.

This is a quick-fix for #2624, where we close the connection if a client
exceeds MAX_FRAME_SIZE. More proper handling with draining the rest of
the frame for the specific frames types that allow it (rfc7540 section
4.2) to come later.

Fixes: #2624

Fixes #2617

Instead of allocating struct h2_sess out of the same workspace that is
used as our rxbuffer, we rather keep it on the stack in h2_new_session.

If the size of the initial h/2 request payload is close to half the size
of the workspace, we would end up exhausting the workspace in HTC_RxInit
after allocating our h2sess struct.

Spotted by Federico G. Schwindt

Fixes: #2619

Ref #2645 but cannot be the cause because workspace is just not
overflowed