Spread attributes behaves not like compiled

[cvlab]

Describe the bug
This bug is already described in a few places, #3067, #1434, #3235, I added comment at the end of #1434

Expected behavior
In special, spread attributes to be deleted on undefined or null values.
In general, spread attributes to behave similar to not spread (at runtime).

Severity
Low to medium.

Additional context
Some attributes are deleted with node.removeAttribute() when the value is undefined or null (but not spread attributes)
spread attributes use set_attributes

svelte/src/runtime/internal/dom.ts

Line 104 in 7de5d6c

node[key] = attributes[key];

for undefined and null

(worst case <input { ...{ size: undefined} } >)

Before #3346 data attributes has to use dataset (but not spread attributes).

Maybe some other rules are not used for spread attr?

Thank you!

[Conduitry]

#1434 was for non-spread attributes. Spread attributes need to be handled differently, because we can't just look up at compile time whether we should be using an attribute or a property.

Is there any difference between this issue and #3067 besides the amount of additional information present? Could this have been a comment on that issue?

[cvlab]

@Conduitry #1434 was for both spread and non-spread. I commented there.

I opened this issue because of idea to check all cases of inconsistency between compiled and runtime spread attributes rules.

Even better is to prevent inconsistency, but this may not be possible.

[Conduitry]

Duplicate of #3067.