feat: add optional compiler-ignore attribute to <slot>

[dane-skipper]

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Tests

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Reason for existence

Closes #8056.
This PR adds an ability to tell Svelte to not compile a <slot> into a Slot so that a developer using Svelte can optionally choose to use a <slot> with behavioral characteristics as defined in the Web Component spec.
Changes are non-breaking, and test execution should reflect that.
Docs have also been updated.

A note on implementation design

There seemed to be a number of places where the compiler-ignore Attribute could have been evaluated and operated upon (e.g. during parsing).
To me, it seemed best to do so during compilation, immediately before the selection of the constructor, through which a given Node would get compiled.

[baseballyama]

I don't think we should add such an option because already we can use a native slot if we use <svelte:element this="slot">.
Personally, we should have only one way to achieve one thing.

So my opinion is that how about adding documentation about it?

[dane-skipper]

I was unaware of that option -- thank you for pointing that out! I also agree with the point of only having one way to do things.
I'll revise this PR to only add relevant documentation

[baseballyama]

We discussed that we will update only the docs in this PR.
So until updating this point, I will change the status to draft.

[baseballyama]

close in favor of #8326.
(I tried to push a new commit but I don't have permission, so I created a new PR.)