Add update script migrating location fields to 7.0

[edalzell]

Final piece of #190 — customers upgrading to 7.0 shouldn't hand-edit content.

src/UpdateScripts/MigrateLocationFields.php, same pattern as ConvertConfigToSettings: shouldUpdate() → $this->isUpdatingTo('7.0').

Migration

Iterate entries in Events::setting('collections'), all localizations. Events-owned handles only → nested location group shape from #195:

Old	New
address (string)	location.name
non-URL string location	location.name
URL string location	online_url
link	online_url
top-level coordinates	location.coordinates

Then remove the old handles. Preserve an existing online_url if already set when migrating link / URL-location.

Never touch a non-string / foreign location. Array-shaped values belong to Prime/Simple (details, etc.) — Prime migrates in transformstudios/prime#834. Log entry IDs and skip.

Ambiguous cases — log and skip (list IDs):

• address and a non-URL string location both set (today address wins for LOCATION:)
• link and a URL-valued location both set
• online_url already set and a conflicting link / URL-location

Tests

TDD. tests/UpdateScripts/MigrateLocationFieldsTest.php:

• each row moves to the nested / online_url target; old handles removed
• ambiguous cases logged, entry untouched
• array-shaped location untouched
• top-level coordinates move under location.coordinates
• multi-site localizations
• shouldUpdate() true for 6→7 and 5→7; false within 6.x or 7.x

Docs

Finish 7.0 upgrade notes from #195: what migrates, what skips, back-up-first, computed-value mappings are manual.

Branch

feature/migrate-location-fields off main. Needs #195.

Part of #190.