CustomSelectControl V2: fix trigger text alignment in RTL languages

[ciampo]

What?

Part of #55023

Allow the text on the CustomSelectControlV2 trigger button to follow RTL text alignment.

Why?

Following user preferences when using the component in a RTL environment

How?

Using logical properties instead of physical (text-align: start instead of text-align: left)

Testing Instructions

• Load storybook examples for CustomSelectControlV2
• Via the Storybook top toolbar controls, change the text direction from LTR to RTL
• Observe how the select trigger button label aligns correctly to the right (while on trunk is would stay on the left)

Screenshots or screencast

Before (trunk)	After (this PR)

[github-actions]

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Co-authored-by: ciampo <mciampini@git.wordpress.org>
Co-authored-by: mirka <0mirka00@git.wordpress.org>

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[mirka]

Good catch, thanks 🙏

[github-actions]

Flaky tests detected in d524d09.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/9683547164
📝 Reported issues:

• [Flaky Test] submenu click on the arrow interactions #61884 in /test/e2e/specs/editor/blocks/navigation-frontend-interactivity.spec.js