return cached value for call id instead of calling AIDL

ImsCallSession#getCallId() calls vendor side getCallId() via AIDL, which may cause unexpected deadlock between AOSP FWK and Vendor Ims service

Bug: 269586572
Test: E2E Call test with log trace
Change-Id: I63dd416bd5b3158e0bd08e1f016973a5622af6a6