Expose FlushAndTearDown API in C-API

[shivpratap1992]

No description provided.

[lalitb]

Can you also add a unit test at:

cpp_client_telemetry/tests/functests/APITest.cpp

Line 619 in 6129741

TEST(APITest, C_API_Test)

Basically calling this API just before evt_close atleast to ensure there is no crash from the API.

[lalitb]

Thanks.

[maxgolov]

@shivpratap1992 @lalitb

I think this fix is doing something wrong : evt_close does ref-counting and performs FlushAndTeardown when necessary, when the last instance is gone. In host-guest scenarios, when two entities are anchored to the same LogManager instance - allowing one of them to explicitly destroy the LogManager via FlushAndTeardown may lead to catastrophic results. For example, in case if guest calls the teardown C API before host app.

Was there an issue with evt_close not properly invoking the teardown sequence?