(This is a merge of http://go/wvgerrit/134312.)
This patch fixes code that would trigger -Wshorten-64-to-32 by
implicitly narrowing a variable from 64 to 32 bits. Most of the time, it
does this by making the implicit conversion explicit. There are a lot of
these places in the usage table code because we always use uint32_t as
the type of a usage entry index, but much of the code that interacts
with the usage table system naturally wants to use size_t.
Bug: 194971260
Test: OEMCrypto unit tests
Test: x86-64 platform tests
Change-Id: I3923af40715efe367955a194a9e33be3e9cb014c