FTL: Add FTL_EXPECT

Like FTL_TRY, FTL_EXPECT unwraps T for Expected<T, E> or does an early
out on error, but it bails out with E instead of Expected<T, E>.

Fix a line in the Expected.Try test to call the intended helper.

Bug: 185536303
Test: ftl_test
Change-Id: I238ae2978ff606c5c035e9791496c2b20729ca7f