Reorder ImsFeature initialization to handle STATE_READY

The method ImsFeature#setFeatureState can not be called
in the constructor of MmTelFeature currently, because the
IMS_SERVICE_UP intent will not be sent until mContext != null.

Remove this dependency and ensure addImsFeatureStatusCallback
is called after ImsFeature#initialize.

Bug: 130569556
Test: atest GtsTelephonyTestCases; atest FrameworksTelephonyTests
Change-Id: Ib3ca59eeeda89c0989cfd767257a6a598a97a670