Add isEuiccSupportedCountry system API to EuiccManager

Currently LPA passed supported/unsupported countries to Settings by
writing the value into properties which is not ideal. Instead, we need to
provide an API in EuiccManager to determine whether eUICC is supported
in a country.
Bug: 147674689
Test: 1) Manually tested by flashing the change to the device
2) Change LPA to override onGetIsEuiccSupportedCountry
3) Make sure LPA can get the request

Change-Id: I01c7df59a6257eb908bc179c5491ca371daa154d
Merged-In: I01c7df59a6257eb908bc179c5491ca371daa154d