Show fusion nodes inline in HLO graph dumper.

To make this work sanely I had to change NodeFilter so that it says to
dump all nodes inside subcomputations.  Previously, we passed an
explicit NodeFilter down to DumpSubcomputation, and used that to control
whether or not we dumped nodes in there.  But this becomes unwieldy with
inline fusion nodes, as sometimes you want to look at 'filter', and
other times you want to look at 'filter_', and there's no good way to
tell why.

I also had to remove the heuristic whereby we'd pull in operands of
nodes with just some operands shown.  With the much bigger nodes that
are generated by this change, the graph was becoming illegible.  I think
most of the confusion that heuristic was attempting to avoid is
addressed by the fact that we "gray out" incomplete nodes.

PiperOrigin-RevId: 163091423