Fix Dialog to have `--salt-zIndex-modal`

[origami-z]

Dialog to have modal z-index. Scrim remains as Drawer zindex - 1, given Drawer also uses it.

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Name	Status	Preview	Comments	Updated (UTC)
saltdesignsystem	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Sep 2, 2024 2:35pm

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🦋 Changeset detected

Latest commit: 0d38e1d0ed986090e5d72170d97ce93b6d737a7e

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

This PR includes changesets to release 1 package

| Name | Type | | ------------- | ----- | | @salt-ds/core | Patch |

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