fix: allow arbitrary content in <select> elements

[Rich-Harris]

Until recently there were restrictions on what content could appear inside <select> and <option> elements. That's no longer true, and so we should probably drop the compiler errors that prevent people from building customizable selects.

Closes #15617

Before submitting the PR, please make sure you do the following

• 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
• Prefix your PR title with feat:, fix:, chore:, or docs:.
• This message body should clearly illustrate what problems it solves.
• Ideally, include a test that fails without this PR but passes with it.
• If this PR changes code within packages/svelte/src, add a changeset (npx changeset).

Tests and linting

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

[changeset-bot]

🦋 Changeset detected

Latest commit: fdb66fe

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

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@16903

[paoloricciuti]

This is not possible right now...only the parser in chrome will persist element within the select, the same code will work in chrome and fail hydration on safari and Firefox. We need to add runtime logic to branch based on CSS.support and build both hydration marching

[paoloricciuti]

Requesting change to prevent accidental merge

[7nik]

As I have written in the issue, it is much deeper. Also, there is a simple workaround of using components/snippets to mask the "non-allowed" content.

[paoloricciuti]

The workaround still fucks up hydration tho