Improve the performance to avoid the potential ANR

The operation of onReceive may take a longer time than expected,
which can be posted to the handler thread to prevent the potential
ANR. The synchronized block is not necessary and can be replaced
by the concurrent collection.

Flag: EXEMPT bugfix
Bug: 369750121
Test: atest TelecomUnitTests:DefaultDialerCacheTest
Change-Id: Id30792c9bf3d32a813c4d2eb27dda350139bb93e