refactor(select): hide empty option for placeholder and floating label right away

[mfranzke]

Proposed changes

As a follow up to #5888, we should even already hide the first, empty option that we're inserting for placeholder and floating label DBSelect components, right away, in case that showEmptyOption is defined. That for we use the :open CSS pseudo selector as progressive enhancement.

As soon as :open is supported widely (only Safari is missing support currently, but will release it most likely with version 26.5), we could even also remove the first part of this :has selector.

Types of changes

• Bugfix (non-breaking change that fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (improvements to existing components or architectural decisions)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Further comments

🔭🐙🐈 Test this branch here: https://design-system.deutschebahn.com/core-web/review/refactor-select-hide-our-empty-option-right-away

[changeset-bot]

🦋 Changeset detected

Latest commit: 1027973

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

This PR includes changesets to release 12 packages

Name	Type
@db-ux/core-components	Minor
@db-ux/ngx-core-components	Minor
@db-ux/v-core-components	Minor
@db-ux/wc-core-components	Minor
@db-ux/react-core-components	Minor
@db-ux/core-foundations	Minor
@db-ux/core-stylelint	Minor
@db-ux/core-migration	Minor
@db-ux/agent-cli	Minor
@db-ux/core-eslint-plugin	Minor
@db-ux/core-vite-plugin	Minor
@db-ux/core-postcss-plugin	Minor

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