fix(cleanupIds): handle when 2 ids referenced in one attr

[SethFalco]

The cleanupIds plugin was only checking for the first reference to an ID in any given attribute. If the attribute referenced a second ID, that reference wouldn't be counted.

This resulted in nodes being removed wrongfully because we missed where it was referenced due to backing out early.

• Updates the regReferencesUrl regex to be global, and we iterate results instead of take the first only.
• No longer copies the attribute value before iterating, as this can mutate between iterations.

Metrics

With only cleanupIds enabled.

SVG	time	% reduced	final size	borked
Original			7.462 KiB
v3.0.2	6 ms	16.4%	6.239 KiB	borked
main (82593c6)	6 ms	16.4%	6.239 KiB	borked
this branch	6 ms	16.5%	6.233 KiB

With only preset-default enabled.

SVG	time	% reduced	final size	borked
Original			7.462 KiB
v3.0.2	26 ms	69.6%	2.267 KiB	borked
main (82593c6)	24 ms	69.6%	2.267 KiB	borked
this branch	23 ms	67.8%	2.403 KiB

Related

• Closes gradients are lost in compression #1722