`<svelte:head>` duplicate tags when using `+layout.svelte`

Describe the bug

This is similar to https://github.com/sveltejs/kit/issues/6858, https://github.com/sveltejs/svelte/issues/4533, https://github.com/sveltejs/svelte/issues/6463, https://github.com/sveltejs/svelte/issues/7444 but is SvelteKit specific.

When using <svelte:head> in +layout.svelte, some tags are duplicated when then using <svelte:head> on other pages. It looks like <title> is de-duped successfully, but other meta tags slip through, giving duplicates.

This is a problem for me when working with Opengraph tags - my hope was that the last tag attributed would just be picked up when sharing a link, but that doesn't seem to happen, and it's always picking up the first meta tag it finds instead. Since SvelteKit already elegantly handles duplicate <title> tags it feels like this is a bug, and that it should also account for duplicate <meta> tags too.

Potential work around here of course is just to define <svelte:head> in each individual page file, but this isn't ideal DX.

Reproduction

https://www.sveltelab.dev/eq6abubatgq8jn1

Logs

No response

System Info

System:
    OS: macOS 13.3.1
    CPU: (8) arm64 Apple M1 Pro
    Memory: 103.92 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 18.12.1 - ~/.nvm/versions/node/v18.12.1/bin/node
    Yarn: 1.22.19 - ~/.nvm/versions/node/v18.12.1/bin/yarn
    npm: 8.19.2 - ~/.nvm/versions/node/v18.12.1/bin/npm
  Browsers:
    Brave Browser: 113.1.51.110
    Chrome: 113.0.5672.126
    Safari: 16.4
  npmPackages:
    @sveltejs/adapter-auto: ^2.1.0 => 2.1.0 
    @sveltejs/kit: ^1.20.1 => 1.20.1 
    svelte: ^3.59.1 => 3.59.1 
    vite: ^4.3.9 => 4.3.9

Severity

annoyance

Additional Information

No response

Start with the linked SvelteLab reproduction and compare head output from +layout.svelte with output from individual page files. Trace the SvelteKit handling of svelte:head and verify that the completed fix prevents duplicate meta tags while preserving the existing title behavior.