trace_processor: fix overflow in bitvector
trace_processor: fix overflow in bitvector

block_index should allowed to be a uint32 as we have bitvectors which
are more than 35 million bits which is the max extent of uint16 with the
current block size.

Bug: 147844721
Change-Id: Ie781cb1a9aa7d09e419cb3ea488c955fee5c60b4
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto