Print nodes without ID in --query-all

[emersion]

This can be useful to figure out the bounding box of an SVG document.

Alternative to #1050

[luisbg]

Both of these are by @emersion and #1100 is explicitly an alternative to #1050, so I think we should pick one. Both merge clean and pass the suite.

#1050 prints the document bbox directly. #1100 prints every node's bbox and the caller unions them, it never prints the root, so it doesn't directly answer "what's the document bbox". It also changes --query-all output contract, though ID'd lines keep their content and order.

I personally prefer #1050 as additive with no compat risk, but changing the --query-all output is a policy call.

@LaurenzV @nicoburns , preference?

[LaurenzV]

Closing in favor of #1050.