[6.x] Backdrop blur for modals

[jaygeorge]

Description of the Problem

We previously removed some modal blurs because it obscured useful content. This came up again in #13905 because the blur on delete modals hid useful information like which entries you were trying to delete.

What this PR Does

Closes #13905 …

Blurred modals keep causing unintended consequences so I think it's better to default to blur = off for confirmation modals, and consciously turn it on when it makes sense.

I've updated the confirmation modals so that blur is off by default and mapped out where to turn them on:

Blur ON

File	Modal / purpose
components/LicensingAlert.vue	License snooze (Licensing Alert)
components/two-factor/TwoFactor.vue	Disable 2FA confirmation
components/modals/ElevatedSessionModal.vue	Elevated session (password/code)
components/two-factor/RecoveryCodesModal.vue	Recovery codes, Regenerate "Are you sure?"
components/two-factor/Setup.vue	Set up Two Factor Authentication
pages/users/Passkeys.vue	Error modal, Create a Passkey
components/updater/Release.vue	Update to :version
components/command-palette/CommandPalette.vue	Command palette (hardcoded overlay)

Blur OFF

File	Modal / purpose
pages/utilities/Cache.vue	Invalidate Static Cache (URLs)
components/ui/Listing/CustomizeColumns.vue	Customize Columns
components/fieldtypes/replicator/SetPicker.vue	Set picker (grid mode)
components/ui/Listing/Presets.vue	Create New View, Rename View, Delete View
components/fieldtypes/replicator/Set.vue	Delete Set
components/fieldtypes/grid/Grid.vue	Delete Row
components/fieldtypes/TableFieldtype.vue	Delete Row, Delete Column
components/fieldtypes/ArrayFieldtype.vue	Delete Row
components/fieldsets/FieldsetDeleter.vue	Delete fieldset
components/fieldsets/FieldsetResetter.vue	Reset fieldset
components/blueprints/BlueprintResetter.vue	Reset blueprint
components/ResourceDeleter.vue	Delete resource (e.g. assets, containers)
components/collections/DeleteLocalizationConfirmation.vue	Delete localization
pages/preferences/nav/Edit.vue	Reset nav, Remove nav section
components/actions/ConfirmableAction.vue	Action confirmations (e.g. delete asset)
components/assets/Upload.vue	New filename
components/field-actions/FieldActionModal.vue	Field action confirmation
components/entries/PublishForm.vue	Create localization, Unsaved changes
components/terms/PublishForm.vue	Unsaved changes
components/globals/PublishForm.vue	Unsaved changes
components/inputs/relationship/InlinePublishForm.vue	Unsaved changes (discard)
components/structures/PageEditor.vue	Unsaved changes (discard)
components/structures/PageTree.vue	Discard changes
components/revision-history/Restore.vue	Restore revision
pages/layout/Layout.vue	Copy to clipboard
components/assets/Editor/Editor.vue	Unsaved changes (discard)
pages/Playground.vue	Demo modal

How to Reproduce

1. View various modals, e.g. delete an entry in a collection.