Umbraco 17.7 readiness: property move tests and culture casing

[KevinJump]

Works through #1067. Every test passes against both Umbraco 17.3.0 (our floor) and 17.7.0: 172 of 172.

Changes

Property moves (umbraco/Umbraco-CMS#23493). 17.7 fixes MovePropertyType(alias, null) orphaning the property, which broke MoveToNull_OrphansTheProperty (it asserted the bug). The re-home workaround stays because 17.3–17.6 still need it; on 17.7 it does nothing. The move logic moves into an internal helper so the tests call the real code. Integration tests now save and reload moves in both directions. null! stays, since the parameter only accepts null from 17.7.

Culture casing (umbraco/Umbraco-CMS#23425). A language stored as da-dk used to export as da-dk everywhere. On 17.7 the name and published cultures become da-DK while property values stay da-dk. Culture codes are now written in standard casing on export (names, values, published, schedule), so output is the same on every 17.x. For the release notes: sites with odd-cased language codes will see a one-off change to their files on the next export.

Checked, no change needed

• First boot and the cache rebuild (#23533, #23709). No 17.x migration requests a rebuild. v13 uSync used the same plan name and Umbraco compares plan states ignoring case, so existing sites never re-run first boot. The import is unscoped, so each save updates the cache, and UnattendedUpgrader refreshes the published snapshot after package migrations on 17.3 and 17.7 alike.
• Invalid or uninstalled cultures on import. They behave the same on 17.3 and 17.7: the handler catches the error and reports a normal import failure. Tests added.

Refs #1067

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