Existing code was assuming that 'lexical' blocks were the same as basic
blocks, therefore code which emitted jumps within a lexical block (e.g.,
logical or) would in some occassions incorrectly omit a necessary
ToBoolean.

This change removes Enter/LeaveBlock from BytecodeArrayBuilder and
instead tracks basic blocks via label bindings and jump operations. The
change also ensures we don't emit dead code at the end of a basic block,
and adds tests of the edge cases.

BUG=v8:4280
LOG=N

Review URL: https://codereview.chromium.org/1406983010

Cr-Commit-Position: refs/heads/master@{#31741}