UTS: rename uts/objects to uts/liveobjects, per the PDR-080 product naming #566

The UTS specifications for LiveObjects live under uts/objects/, and their files carry the same prefix (objects_gc_test.md, objects_lifecycle_test.md, objects_sync_test.md, proxy/objects_faults.md). PDR-080 (SDK and plugin naming conventions) puts the product name in repository, package and import names and keeps the resource name for the API: @ably/liveobjects and AblyLiveObjects, but channel.objects. The test directory sits on the package side of that line, so it reads as a different name for the product.

It matters because SDKs mirror the directory. ably-js has test/uts/objects/ and ably-cocoa has Test/UTS/integration/standard/objects/ and .../proxy/objects/. ably-python (ably/ably-pubsub-python#731) has test/uts/objects/ beside an implementation package that is now ably.pubsub.liveobjects, which a reviewer there flagged as misleading. Each SDK keeps the mirror so that a test file maps onto its specification, so the rename has to start here.

Proposal: rename uts/objects/ to uts/liveobjects/, and the objects_* file names to match, then have the SDKs follow. Feature IDs (RTO, RTLM and so on), objects-features.md and the API names they describe are out of scope; they are resource names under PDR-080.

Related: #377, which renames the plugin under the same decision.