Allow concurrent WearableSensingService connections

The enforcement for max concurrent connection limit will be added in a
follow-up change shortly after this.

The old provideConnection API will be deprecated in a separate CL
because deprecation cannot be flagged and can only be done after 25Q2
becomes next.

Bug: 358133158
Flag: android.app.wearable.enable_concurrent_wearable_connections
Test: atest CtsWearableSensingServiceTestCases after patching ag/29937309
Change-Id: I2a71d2f1d4e0d1ad1db1c3a251fbacaa91e0abba