fix: Add missing plaintext-only value to contenteditable type

[vhladko]

Svelte compiler rewrite

As it was mentioned in #9181 contenteditable property was incomplete and missing 'plaintext-only'. This PR actually add this value to type.

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• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
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Tests and linting

• Run the tests with pnpm test and lint the project with pnpm lint

[changeset-bot]

🦋 Changeset detected

Latest commit: e479d04

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
svelte	Patch

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[jasonlyu123]

As the bot mentioned, This needs a changeset.

[vhladko]

As the bot mentioned, This needs a changeset.

my bad, just added :)

[vhladko]

@jasonlyu123 can it be merged ?

[dummdidumm]

Thank you!