Avoid astro:assets symbol collisions in language tools

[VenkataAllu15]

Summary

• keep generated Astro component identifiers internal in the language server and TS plugin
• add a regression test for image.astro importing Image from astro:assets
• avoid the virtual TSX name collision that produced Import declaration conflicts with local declaration of "Image"

Closes #14683

Testing

• pnpm --filter @astrojs/language-server test --match Diagnostics
• pnpm --filter @astrojs/ts-plugin build

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