fix: error on duplicate style and class directive

[paoloricciuti]

Svelte 5 rewrite

Closes #13095

I've also left a comment about the rest of the directives since i fell in the trap of try to add those tho only to discover they were already handled.

UPDATE: linting fortunately caught something i didn't realised could've been a problem. Something like this

<div draggable={true} class:draggable={true} />

Should actually be allowed, so i've fixed this bug...i've slightly modified the test runner to assert that a code should not produce compiler errors so that i was able to also test for this. Let me know if it's not what we want, i can move the test in another suite but it seemed something that could be useful. scratch that, after a chat with Simon i moved the test to validator and reverted the changes.

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